Information recording medium, reproducing apparatus thereof and recording apparatus thereof

ABSTRACT

An information recording medium  1  at least comprises a substrate  13  having a microscopic pattern  20,  which is constituted by a shape of continuous substance of approximately parallel grooves formed with a groove section G and a land section L alternately, a recording layer  12  formed on the microscopic pattern  20  and a light transmission layer  11  formed on the recording layer. The microscopic pattern  20  is formed so as to satisfy a relation of P&lt;λ&lt;NA and a thickness of the light transmission layer  11  is within a range of 0.07 to 0.12 mm, wherein P is a pitch of the groove section G or the land section L, λ is a wavelength of reproducing light beam and NA is a numerical aperture of an objective lens. Further, there provided an information recording medium, which is improved in cross erase and recorded in high density, and a reproducing apparatus and a recording apparatus for the information recording medium.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an information recording medium,a reproducing apparatus and a recording apparatus, which read outinformation from the information recording medium with making it moverelatively, particularly, relates to an information recording medium tobe recorded and/or reproduced through an optical device, and areproducing apparatus and a recording apparatus for such an informationrecording medium.

[0003] 2. Description of the Related Art

[0004] Until now, there is existed a system for reading out informationfrom an information recording medium, which is made relatively move. Insuch a system, reproduction is performed by using a device such as anoptical device, a magnetic device and a capacitive device. A system,which records and/or reproduces by an optical device, is usedextensively in daily living. With respect to a read only informationrecording medium to be reproduced by using a light beam having awavelength λ of 650 nm, for example, mediums such as a DVD (DigitalVersatile Disc) Video prerecorded with video information, a DVD-ROM(Digital Versatile Disc-Read Only Memory) prerecorded with a program orlike, and a DVD Audio disc and an SACD (Super Audio Compact Disc)prerecorded with musical information are well known.

[0005] Further, there is provided a DVD-R (Digital VersatileDisk-Recordable) as a recordable recording and reproducing typeinformation recording medium, which uses dye. Furthermore, there isprovided a DVD-RAM (Digital Versatile Disc-Random Access Memory), aDVD-RW (Digital Versatile Disk-ReWritable) and a DVD+RW (DigitalVersatile Disk+ReWritable) as a recording and reproducing typeinformation recording medium, which use phase change. Moreover, there isprovided an ASMO (Advanced Storage Magneto-Optical) disc, an ID(intelligent image) disc and a GIGAMO (GIGA-byte Magneto-Optical) discas a recording and reproducing type information recording medium usingphoto-magnetism.

[0006] On the other hand, in order to increase recording density of aninformation recording medium, a study for shortening a wavelength oflaser beam has been continued for a long period of time. A secondharmonic generating element invented recently and a semiconductor lightemitting element composed of gallium nitride system compound (disclosedin the Japanese Patent No. 2778405, for example), emit light having awavelength λ of approximately 350 to 450 nm. Consequently, theseelements can become an important light emitting element, which increasesa recording density sharply.

[0007] In addition thereto, design for an objective lens coping withsuch a wavelength has been advanced, particularly, a lens having anumerical aperture (NA) of more than 0.7, which exceeds the NA 0.6utilized for a DVD disc, is currently developed.

[0008] As mentioned above, a reproducing apparatus for an informationrecording medium having capability such that a wavelength λ is shortenedto 350 to 450 nm and an NA is more than 0.7 has been developing. It isexpected that an optical disc system, which has a higher recordingdensity extremely exceeding that of a current DVD disc, can be developedby using these techniques.

[0009] By using such a light beam having a shorter wavelength than onefor a DVD disc and a lens having a higher NA, an information recordingmedium having an extremely higher recording density can be realized.However, coma aberration also increases extremely when an informationrecording medium is slanted. Consequently, an information recordingmedium of which thickness for light transmission is made extremelythinner than that of a DVD disc is required. Actually, a disc systemcalled a “DVR land groove” has been proposed. In the disc system, byusing a light emitting element having a wavelength of 405 nm and anobjective lens having an NA of 0.85, a thickness of disc for lighttransmission is designed for 0.1 mm.

[0010] With referring to FIGS. 1 and 2, a conventional informationrecording medium is explained.

[0011]FIG. 1 is a cross sectional view of a conventional informationrecording medium according to the prior art.

[0012]FIG. 2 is a fragmentary plan view, partially enlarged, of theconventional information recording medium shown in FIG. 1.

[0013] As shown in FIG. 1, an information recording medium 100 iscomposed of a recording layer 120 and a light transmission layer 110,which are laminated on a substrate 130 in order. The substrate 130 isformed with a microscopic pattern 200. The recording layer 120 is formedon the microscopic pattern 200 directly. The microscopic pattern 200 hasmicroscopic patterns composed of land sections L1 and L2 (hereinaftergenerically referred to as “land section L”) and groove sections G1through G3 (hereinafter generically referred to as “groove section G”).

[0014] While recording, as shown in FIG. 2, a record mark M is formed onboth the land section L and the groove section G (it is called aland-groove recording method.)

[0015] With paying attention to dimensions of the microscopic pattern200, with defining that a minimum distance between the centers ofadjacent groove sections G is a pitch P (a minimum distance between thecenters of adjacent land sections L is also the pitch P), the landsection L and the groove section G are formed so as to satisfy arelation P>S with respect to a reproduction spot diameter S of a lightbeam.

[0016] Further, the reproduction spot diameter S can be calculated by anequation S=λ/NA, where λ is a wavelength of a laser beam forreproduction and NA is a numerical aperture of an objective lens. Inother words, the pitch P is designed in order to satisfy a relationP>λ/NA.

[0017] In the information recording medium 100, an information recordedin the recording layer 120 is read out by irradiating a reproducinglight beam incident on the light transmission layer 110. The informationis taken out through the light transmission layer 110 after thereproducing light beam has been reflected by the surface of therecording layer 130 and reproduced.

[0018] The inventors of the present invention performed an experimentfor recording and reproducing the information recording medium 100actually manufactured by using a light emitting element radiating alight beam having a single wavelength within a range of 350 to 450 nmand an objective lens having a higher NA of 0.75 to 0.9, and then it isfound that a cross erase phenomenon was remarkable.

[0019] The cross erase phenomenon is a phenomenon such that aninformation to be recorded in a land section L, for example, is recordedin a groove section G with overlapping a signal previously recorded inthe groove section G when recording the information in the land sectionL. In other words, it is such a phenomenon that an informationpreviously recorded in a groove section G is erased by recording anotherinformation in a land section L.

[0020] Further, this phenomenon can also be noticeable in a reversecase. That is, the cross erase phenomenon is also recognized if apreviously recorded information in a land section L is observed whenrecording an information in a groove section G.

[0021] If the cross erase phenomenon occurs, as mentioned above, aninformation recorded in an adjacent track is damaged. In a case of aninformation system having larger capacity, an amount of lost informationbecomes excessively large. Consequently, affection to a user isenormous. Therefore, it is considered for such an information recordingmedium 100 that an information shall be recorded only in either landsection L or groove section G. However, recording capacity of aninformation recording medium will decrease and a merit of theinformation recording medium having a potential of recording in higherdensity will decline.

SUMMARY OF THE INVENTION

[0022] Accordingly, in consideration of the above-mentioned problems ofthe prior art, an object of the present invention is to provide aninformation recording medium, which is improved in the cross erasephenomenon and recorded in a higher density, and a reproducing apparatusthereof and a recording medium thereof.

[0023] Particularly, an object of the present invention is to provide aninformation recording medium with assuming that it is recorded andreproduced by a light beam having a wavelength of 350 to 450 nm and areproducing apparatus and a recording apparatus thereof.

[0024] In order to achieve the above object, the present inventionprovides, according to an aspect thereof, an information recordingmedium, which at least comprising: a substrate having a microscopicpattern, which is constituted by a shape of continuous substance ofapproximately parallel grooves formed with a groove section and a landsection alternately; a recording layer formed on the microscopicpattern; and a light transmission layer formed on the recording layer,the information recording layer is characterized in that the microscopicpattern is formed so as to satisfy a relation of P<λ<NA and a thicknessof the light transmission layer is within a range of 0.07 to 0.12 mm,wherein P is a pitch of the groove section or the land section, λ is awavelength of reproducing light beam and NA is a numerical aperture ofobjective lens.

[0025] According to another aspect of the present invention, thereprovided a reproducing apparatus, which reproduces an informationrecording medium at least comprising: a substrate having a microscopicpattern, which is constituted by a shape of continuous substance ofapproximately parallel grooves formed with a groove section and a landsection alternately; a recording layer formed on the microscopicpattern; and a light transmission layer formed on the recording layer,wherein the information recording layer is characterized in that themicroscopic pattern is formed so as to satisfy a relation of P<λ<NA anda thickness of the light transmission layer is within a range of 0.07 to0.12 mm, and wherein P is a pitch of the groove section or the landsection, λ is a wavelength of reproducing light beam and NA is anumerical aperture of objective lens, the reproducing apparatuscomprising:

[0026] a pickup composed of a light emitting element having a wavelengthof λ within a range of 350 to 450 nm and an objective lens having anumerical aperture of NA within a range of 0.75 to 0.9 for reading outreflected light from the information recording medium; a motor forrotating the information recording medium; a servo device forcontrolling to drive the pickup and the motor; a turntable forsupporting the information recording medium while rotating; ademodulator for demodulating an information signal read out by thepickup; an interface (I/F) for transmitting a signal demodulated by thedemodulator externally; and a controller for controlling the reproducingapparatus totally.

[0027] According to further aspect of the present invention, thereprovided a recording apparatus for recording an original informationsignal on an information recording medium at least comprising: asubstrate having a microscopic pattern, which is constituted by a shapeof continuous substance of approximately parallel grooves formed with agroove section and a land section alternately; a recording layer formedon the microscopic pattern; and a light transmission layer formed on therecording layer, wherein the information recording layer ischaracterized in that the microscopic pattern is formed so as to satisfya relation of P<λ<NA and a thickness of the light transmission layer iswithin a range of 0.07 to 0.12 mm, and wherein P is a pitch of thegroove section or the land section, λ is a wavelength of reproducinglight beam and NA is a numerical aperture of objective lens, therecording apparatus comprising: a pickup composed of a light emittingelement having a wavelength of λ within a range of 350 to 450 nm and anobjective lens having a numerical aperture of NA within a range of 0.75to 0.9 for reading out reflected light from and recording on theinformation recording medium; a motor for rotating the informationrecording medium; a servo device for controlling to drive the pickup andthe motor; a turntable for supporting the information recording mediumwhile rotating; an interface (I/F) for receiving the originalinformation signal to be recorded; a modulator for modulating theoriginal information signal; a waveform converter for converting theoriginal information signal into a format suitable for a recordingcharacteristic of the recording layer of the information recordingmedium; an auxiliary information demodulator for demodulating adifferential signal outputted from the pickup; and a controller forcontrolling the recording apparatus totally.

[0028] Other object and further features of the present invention willbe apparent from the following detailed description when read inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

[0029]FIG. 1 is a cross sectional view of a conventional informationrecording medium according to the prior art.

[0030]FIG. 2 is a fragmentary plan view, partially enlarged, of theconventional information recording medium shown in FIG. 1.

[0031]FIG. 3 is a cross sectional view of an information recordingmedium according to a first embodiment of the present invention.

[0032]FIG. 4 is a fragmentary plan view, partially enlarged, of theinformation recording medium shown in FIG. 3.

[0033]FIG. 5 is a cross sectional view of an information recordingmedium according to a second embodiment of the present invention.

[0034]FIG. 6 is a cross sectional view of an information recordingmedium according to a third embodiment of the present invention.

[0035]FIG. 7 is a cross sectional view of an information recordingmedium according to a fourth embodiment of the present invention.

[0036]FIG. 8 is a cross sectional view in partially enlarged of aninformation recording medium according to a fifth embodiment of thepresent invention.

[0037]FIG. 9 is a fragmentary plan view, partially enlarged, of anamplitude modulation address recorded in an information recording mediumaccording to the present invention.

[0038]FIG. 10 is a fragmentary plan view, partially enlarged, of afrequency modulation address recorded in an information recording mediumaccording to the present invention.

[0039]FIG. 11 is a fragmentary plan view, partially enlarged, of a firstphase modulation address recorded in an information recording mediumaccording to the present invention.

[0040]FIG. 12 is a fragmentary plan view, partially enlarged, of asecond phase modulation address recorded in an information recordingmedium according to the present invention.

[0041]FIG. 13 is a table exhibiting a change of fundamental data ofbefore and after a base-band modulation.

[0042]FIG. 14 is a table of definite example exhibiting a change of dataarray of before and after a base-band modulation.

[0043]FIG. 15 is a block diagram of a first reproducing apparatusaccording to the present invention.

[0044]FIG. 16 is a graph exhibiting a relation between modulatedamplitude and error rate.

[0045]FIG. 17 is a graph exhibiting a relation between a reflectivityand an error rate.

[0046]FIG. 18 is a table showing reflectivity and reproductioncharacteristics of embodiments 6 through 12 and comparative examples 4and 5.

[0047]FIG. 19 is a block diagram of a second reproducing apparatusaccording to the present invention.

[0048]FIG. 20 is a block diagram of a recording apparatus according tothe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0049] [First Embodiment]

[0050] With referring to FIGS. 3 and 4, an information recording mediumaccording to a first embodiment of the present invention will beexplained.

[0051]FIG. 3 is a cross sectional view of an information recordingmedium according to a first embodiment of the present invention.

[0052]FIG. 4 is a fragmentary plan view, partially enlarged, of theinformation recording medium shown in FIG. 3.

[0053] In FIG. 3, an information recording medium 1 is at least composedof a recording layer 12 and a light transmission layer 11, which areformed and laminated on a substrate 13 formed with a rugged microscopicpattern 20 in order. Ruggedness of the microscopic pattern 20 is almostin a shape of continuous substance of parallel grooves G1 through G5(hereinafter generically referred to as groove section G), wherein aplurality of land L1 through L4 (hereinafter generically referred to asland section L) is provided between the groove sections G.

[0054] The information recording medium 1 is a read only type medium,which can be reproduced by using an apparatus composed of a lightemitting element radiating a light beam having a single wavelengthwithin a range of 350 to 450 nm and an objective lens having an NA of0.75 to 0.9. Further, a shape of the information recording medium 1 canbe applicable to any shape such as a disc, a card and a strip or tape.Furthermore, it is also applicable to a circular, square or oval shape.Moreover, a hole can be provided thereon.

[0055] In FIG. 4, “M” is a record mark formed on each of the landsections L1 through L4 (hereinafter referred to as land section Lgenerically) while recording. “P” is a pitch distance between thecenters of groove sections G2 and G3 (hereinafter referred to as groovesection G generically). “S” is a spot diameter of reproducing light beam(reproduction spot diameter).

[0056] In the following paragraphs, the substrate 13, the recordinglayer 12 and the light transmission layer 11 will be detailed.

[0057] The substrate 13 is a base having a function of mechanicallyholding the recording layer 12 and the light transmission layer 11formed thereon. With respect to a material of the substrate 13, any oneof synthetic resin, ceramic and metal can be used.

[0058] Typical examples of the synthetic resin are as follows:polycarbonate, polymethyle methacrylate, polystyrene, copolymer ofpolycarbonate and polystyrene, polyvinyl chloride, alicyclic polyolefin,various thermoplastic and thermosetting resins such as polymethylepentene and various energy ray curable resins (including examples ofultraviolet (UV) ray curable resins, visible light curable resins andelectron beam curable resins). They can be used suitably. Further, thesematerials can be applicable to be combined with metal powder or ceramicpowder.

[0059] Further, typical examples of ceramics are as follows: soda limeglass, soda aluminosilicate glass, borosilicate glass and silica glass.Furthermore, a metal plate such as aluminum having no ability for lighttransmission can be used as a typical example of metal.

[0060] In order to support other layers mechanically, thickness of thesubstrate 13 is 0.3 to 3 mm, preferably 0.5 to 2 mm. In a case that theinformation recording medium 1 is shaped in disc, it is most desirableto be designed such that a total thickness including the substrate 13,the recording layer 12 and the light transmission layer 11 becomes 1.2mm so as to be interchangeable with conventional optical discs.

[0061] The recording layer 12 is a thin film layer having a function ofreading out information, recording information or rewriting information.In the recording layer 12, information is recorded in either one sectionof the land section L and the groove section G. A material, whichgenerates a change of reflectivity, a change of refractive index or bothof them, is utilized for the recording layer 12. With respect to amaterial for the recording layer 12, there is provided a phase changematerial, which generates a change of reflectivity or change ofrefractive index or both changes between amorphous and crystal bythermal recording, or a dye material.

[0062] There is provided phase change materials such as Ge—Sb—Te system,Ag—In—Sb—Te system, Cu—Al—Sb—Te system and Ag—Al—Sb—Te system. Theserecording materials can contain one or more elements as an additiveelement within a range of more than 0.01 atomic % and less than 10atomic % in total. Such an additive element is selected out of Cu, Ba,Co, Cr, Ni, Pt, Si, Sr, Au, Cd, Li, Mo, Mn, Zn, Fe, Pb, Na, Cs, Ga, Pd,Bi, Sn, Ti, V, Ge, Se, S, As, Tl and In.

[0063] With respect to compositions of each element, for example, thereis existed Ge₂Sb₂Te₅, Ge₁Sb₂Te₄, Ge₈Sb₆₉Te₂₃, Ge₈Sb₇₄Te₁₈, Ge₅Sb₇₁Te₂₄,Ge₅Sb₇₆Te₁₉, Ge₁₀Sb₆₈Te₂₂ and Ge₁₀Sb₇₂Te₁₈ and a system adding a metalsuch as Sn and In to the Ge—Sb—Te system as for the Ge—Sb—Te system.Further, as for the Ag—In—Sb—Te system, there is existed Ag₄In₄Sb₆₆Te₂₆,Ag₄In₄Sb₆₄Te₂₈, Ag₂In₆Sb₆₄Te₂₈, Ag₃In₅Sb₆₄Te₂₈, Ag₂In₆Sb₆₆Te₂₆, and asystem adding a metal or semiconductor such as Cu, Fe and Ge to theAg—In—Sb—Te system.

[0064] With respect to a dye material, porphyrin dye, cyamine dye,phthalocyamine pigment, naphthalocyamine pigment, azo dye,naphthoquinone dye, fulgide dye, polymethine dye and acridine dye can beused.

[0065] Furthermore, with respect to a material for the recording layer12, a magneto-optical material, which is reproduced by a change of Kerrrotation angle, can also be used. More accurately, alloys composed of anelement such as terbium, cobalt, iron, gadolinium, chromium, neodymium,dysprosium, bismuth, palladium, samarium, holmium, praseodymium,manganese, titanium, erbium, ytterbium, lutetium and tin are used,(wherein an alloy includes a compound such as oxide, nitride, carbide,sulfide and fluoride). Particularly, constituting an alloy of atransition metal, which is represented by TbFeCo, GdFeCo and DyFeCo,with rare earth element is preferable. Moreover, the recording layer 12can be constituted by using an alternate lamination layer of cobalt andplatinum.

[0066] With respect to a forming method of these phase change material,dye material and magneto-optical material, such methods as vacuumdeposition of resister heating type or electron beam type, directcurrent sputtering, high frequency sputtering, reactive sputtering, ionbeam sputtering, ion plating and chemical vapor deposition (CVD) can beused. Further, with respect to a material out of dye materials,particularly, a material solvable by solvent, a liquid phase filmforming method such as dip coating, spin coating, bar coating, knifecoating and roll coating can be used.

[0067] The light transmission layer 11 has a function of transmitting aconverged reproducing light to the recording layer 12 in a condition ofless optical distortion (the reproducing light is shown by an arrow inFIG. 3). For example, by using a reproducing light having a wavelengthλ, a material having a light transmittance of more than 70% with respectto the reproducing light having the wavelength λ, preferably more than80% can be utilized suitably. It is necessary for the light transmissionlayer 11 to be less optical anisotropy. With considering to controlreduction of reproducing light, actually, a material having abirefringence of less than ±100 nm, preferably ±50 nm, more preferably±30 nm by 90-degree (vertical) incident double paths is used.

[0068] Materials having such a characteristic such as polycarbonate,polymethyle methacrylate, cellulose triacetate, polystyrene, copolymerof polycarbonate and polystyrene, polyvinyl chloride, alicyclicpolyolefin and polymethyle pentene an be used the light transmissionlayer 11.

[0069] Further, it can be applicable to the light transmission layer 11that the light transmission layer 11 has a function of protecting therecording layer 12 mechanically and chemically. With respect tomaterials having such a function, a material having higher stiffnesssuch as, for example, transparent ceramics (such as soda lime glass,soda aluminosilicate glass, borosilicate glass and silica glass),thermosetting plastics and energy ray curable resins (such as UV raycurable resins, visible light curable resins and electron beam curableresins) can be suitably used.

[0070] Furthermore, a thickness of the light transmission layer 11 isdesired to be less than 0.120 mm from a point of view that comaaberration can be suppressed when the information recording medium 1 isslanted with respect to a reproducing light beam or recording lightbeam. More, from another point of view of preventing the recording layer12 from a scratch, it is desired to be more than 0.07 mm. In otherwords, the thickness is desired to be within a range of 0.070 to 0.120mm. If a material of the light transmission layer 11 is one of thematerials mentioned above, an index “z” of refraction is 1.45 to 1.7.Therefore, in a case of considering optical factors, a range of idealthickness of the light transmission layer 11 is 0.093 to 0.107 mm.

[0071] Moreover, scattering of thickness in one plane shall be ±0.003 mmat the maximum, desirably less than ±0.002 mm. More desirably, it mustbe less than ±0.001 mm.

[0072] With referring to FIG. 4, the microscopic pattern 20, which isone of the features of the present invention, is explained next.

[0073] As mentioned above, microscopically, the microscopic pattern 20is composed of a continuous substance of almost parallel grooves. On theother hand, macroscopically, it can be formed in any shape such as line,coaxial and spiral.

[0074] As shown in FIG. 4, in the microscopic pattern 20, a raisedportion is the land section L and a sunken portion is the groove sectionG, wherein they are arranged alternately in parallel with each other.

[0075] The groove section G follows the definition of the Table 4.4-1listed in the text “Understanding Optical Disc by this” (edited by theJapan Patent Office, published in 2000 by Japan Institute of Inventionand Innovation). That is to say, in a disc, the groove section G is “asunken groove, which is previously provided spirally or coaxially inorder to form a recording track on a surface of substrate”. Further, theland section L also follows the definition in the same text. That is, ina disc, the land section L is “a raised portion, which is previouslyprovided spirally or coaxially in order to form a recording track on asurface of substrate”, wherein the substrate is equivalent to thesubstrate 13 of the present invention.

[0076] If it is defined that a minimum distance between the centers ofadjacent groove sections G is the pitch P (a minimum distance betweenthe centers of adjacent land sections L is also the pitch P), the landsection L and the groove section G are formed so as to satisfy arelation P<S with respect to the reproduction spot diameter S of a lightbeam, wherein the reproduction spot diameter S is calculated by aequation S=λ/NA, where λ is a wavelength of a laser beam forreproduction and NA is a numerical aperture of an objective lens. Inother words, the pitch P satisfies a relation P<λ/NA. For example, thepitch P is set to be within a range of 250 to 600 nm. If it isconsidered that a HDTV (High Definition Television) picture is recordedfor a period of two hours approximately, the pitch P is desirable to bewithin a range of 250 to 450 nm.

[0077] An appropriate depth of the groove G is within a range of 10 to300 nm, particularly, with considering a wavelength λ of a reproductionoptical system, the depth is suitable within a range of λ/(8z) toλ/(18z), wherein “z” is an index of refraction of the light transmissionlayer 11 at the wavelength λ. In a case of considering that A=405 nm andz=1.6 (polycarbonate), for example, a most suitable range of the depthis within a range of 14 to 32 nm.

[0078] Microscopically, one groove section G and the other groovesection G, one land section L and the other land section G, and thegroove section G and the land section L are in parallel to each otherrespectively. However, in order to embed an analog or digital auxiliaryinformation such as clock and address, these sections can be wobbledvery little.

[0079] For example, it is acceptable that these grooves are recordedwith a single frequency so as to embed clock, and consequently wobbledsinusoidally on the surface of the substrate 13. In order to embed anauxiliary information (sub information) such as address, these groovescan be modulated in amplitude modulation (AM), frequency modulation (FM)or phase modulation (PM) and wobbled in various patterns.

[0080] In other words, at least either one of an area recorded with asingle frequency for clock and a modulation recording area for embeddingaddress can be formed in either the groove section G or the land sectionL. A modulation method for embedding the auxiliary information (subinformation) such as address will be detailed.

[0081] In a case that the information recording medium 1 is shaped indisc, the wobbling mentioned above can be recorded by the CAV (ConstantAngular Velocity) method or the CLV (Constant Linear Velocity) method.Further, with forming zones varying by radius, the ZCAV (Zone ConstantAngular Velocity) method or the ZCLV (Zone Constant Linear Velocity)method of which controlling varies by each zone can also be adopted.

[0082] Furthermore, although it is not shown, the groove section G orthe land section L is cut in pieces over a certain area in order toembed an auxiliary information such as address, an inherent pit can beformed. More, by allocating an inherent pit in the groove section Gadjacent to the land section L, or by allocating the inherent pit in theland section L in adjacent to the groove section G, an auxiliaryinformation such as address can be embedded. Moreover, a hologram or avisible microscopic pattern for identifying the information recordingmedium 1 can be formed in an area other than a recording area.

[0083] In the information recording medium 1, an information recorded inthe recording layer 12 is read out by irradiating a reproducing lightbeam incident on the light transmission layer 11. The information istaken out through the light transmission layer 11 after the reproducinglight beam has been reflected by the surface of the recording layer 13and reproduced.

[0084] The surface itself of the recording layer 12 of the informationrecording medium 1 has a certain degree of reflectivity, so that areproduction can be functioned by the recording layer 12 as it is.However, in order to improve a reflectivity of a reproducing light beamand to add other functions such as increasing a number of rewritings andimproving weather resistance, a reflective layer or a protective layercan be provided in adjacent to the recording layer 12. In additionthereto, materials for the reflective layer and the protective layerwill be detailed.

[0085] Cross erase of the information recording medium 1 of the presentinvention is evaluated in comparison with that of the conventionalinformation recording medium 100.

[0086] The configuration of the information recording mediums 1 and 100are such that the substrates 13 and 130 are polycarbonate resin, therecording layers 12 and 120 are AgInSbTe one of phase change materialsand the light transmission layers 11 and 110 are polycarbonate resin.

[0087] Evaluation is performed as follows: recording a second track andreproducing, recording first and third tracks with a frequency otherthan that of recorded in the second track 10 times, and then measuringan output of the second track once again.

[0088] As a result of the evaluation, by the conventional informationrecording medium 100, cross ease of −5 dB in maximum is observed.However, by the information recording medium 1 of the present invention,cross ease of −2 dB in maximum is observed. That is to say, in theconventional information recording medium 100, an output reduces by 5 dBin comparison with an output of the second track if the first and thirdtracks are not recorded. On the contrary, an output of the informationrecording medium 1 of the present invention reduces by only 2 dB.

[0089] In other words, by using the information recording medium 1according to the present invention, cross erase is improved by 3 dB incomparison with the conventional information recording medium 100.

[0090] According to an aspect of the first embodiment of the presentinvention, as mentioned above, with defining that a pitch between twoadjacent groove sections G or land sections L is “P”, a wavelength oflaser beam is “λ” and a numerical aperture of objective lens is “NA”, aninformation recording medium is constituted such that a microscopicpattern 20 having a relation of “P<λ<NA” is formed and either the landsection L or groove section G is recorded. Accordingly, an informationrecording medium, which is recorded in high density in conjunction withenabling to reduce cross erase, can be obtained.

[0091] [Second Embodiment]

[0092] With referring to FIG. 5, an information recording mediumaccording to a second embodiment of the present invention is explained.

[0093]FIG. 5 is a cross sectional view of an information recordingmedium according to a second embodiment of the present invention.

[0094] In FIG. 5, same compositions as those of the first embodimentshown in FIG. 3 are indicated by the same sign as that of the firstembodiment respectively and their explanations are omitted.

[0095] As shown in FIG. 5, an information recording medium 2 is the sameconfiguration as that of the first embodiment except for the lighttransmission layer 11. A light transmission layer of the secondembodiment is composed of a light transmission layer 11 a and anadhesive light transmission layer 11 b.

[0096] The light transmission layer 11 a is identical to the lighttransmission layer 11 of the first embodiment. On the contrary, theadhesive light transmission layer 11 b is a layer for adhering the lighttransmission layer 11 a to the recording layer 12 firmly and an adhesiveresin having a light transmittance of more than 70%, desirably more than80% for a light beam having a wavelength λ. Such an adhesive resin is asfollows: thermosetting resin, various energy ray curable resin (such asUV ray curable resin, visible light curable resin and electron beamcurable resin), moisture curable resin, plural liquid mixture curableresin and thermoplastic resin containing solvent.

[0097] A thickness of the adhesive light transmission layer 11 b isdesirable to be more than 0.001 mm as a minimum thickness for exhibitingadhesion and less than 0.04 mm in consideration of preventing anadhesive material from stress crack, more desirable to be within a rangeof more than 0.001 mm and less than 0.03 mm. The most desirablethickness is within a range of more than 0.001 mm and less than 0.02 mm.However, in consideration of warp of the total information recordingmedium 2, the thickness is most desirable to be within a range of morethan 0.001 mm and less than 0.01 mm.

[0098] With respect to a coating method of the light transmission layer11 a, such a method as spin coat, splay, dip, blade coat, roll coat,knife coating, screen printing and offset printing can be used.

[0099] The information recording medium 2 of the second embodiment isevaluated for cross erase by the same manner as that of the firstembodiment and an identical result with the first embodiment isobtained.

[0100] Consequently, an identical effect with the information recordingmedium 1 according to the first embodiment can be obtained by theinformation recording medium 2 according to the second embodiment of thepresent invention.

[0101] [Third Embodiment]

[0102] With referring to FIG. 6, an information recording mediumaccording to a third embodiment of the present invention is explained.

[0103]FIG. 6 is a cross sectional view of an information recordingmedium according to a third embodiment of the present invention.

[0104] In FIG. 6, same compositions as those of the first embodimentshown in FIG. 3 are indicated by the same sign as that of the firstembodiment respectively and their explanations are omitted.

[0105] As shown in FIG. 6, an information recording medium 3 is the sameconfiguration as that of the first embodiment except for a resin layer14 formed with a microscopic pattern 21. The information recordingmedium 3 is composed of the resin layer 14 formed with the microscopicpattern 21, a recording layer 12 and a light transmission layer 11,which are laminated on a substrate 13 a in order.

[0106] In the information recording medium 3 according to the thirdembodiment of the present invention, forming the microscopic pattern 21on the resin layer 14 is different from the first embodiment of whichthe microscopic pattern 20 is formed on the surface of the substrate 13.

[0107] A material for the resin layer 14 is as follows: thermosettingresin, various energy ray curable resin (such as UV ray curable resin,visible light curable resin and electron beam curable resin), moisturecurable resin, plural liquid mixture curable resin and thermoplasticresin containing solvent. A light beam for reproducing or recording doesnot reach as far as the resin layer 14, so that there is no restrictionfor a transmittance of material of the resin layer 14. With respect to athickness of the resin layer 14, it is desirable to be less than 0.02 mmin consideration of warp of the information recording medium 3 in total.

[0108] The information recording medium 3 of the third embodiment isevaluated for cross erase by the same manner as that of the firstembodiment and an identical result with the first embodiment isobtained.

[0109] Consequently, an identical effect with the information recordingmedium 1 according to the first embodiment can be obtained by theinformation recording medium 3 according to the third embodiment of thepresent invention.

[0110] [Fourth Embodiment]

[0111] With referring to FIG. 7, an information recording mediumaccording to a fourth embodiment of the present invention is explained.

[0112]FIG. 7 is a cross sectional view of an information recordingmedium according to a fourth embodiment of the present invention.

[0113] In FIG. 7, a same composition as that of the first embodimentshown in FIG. 3 is indicated by a same sign as that of the firstembodiment and its explanation is omitted.

[0114] As shown in FIG. 7, an information recording medium 4 is composedof a pattern transferring layer 15 having a microscopic pattern 22, arecording layer 12, an adhesive light transmission layer 11 a and alight transmission layer 11 b, which are laminated on a substrate 13 bin order.

[0115] Further, in the information recording medium 4 according to thefourth embodiment of the present invention, it is different from thesecond embodiment that the top surface of the substrate 13 b being incontact with the pattern transferring layer 15 is flat, and that themicroscopic pattern 22 is formed on the pattern transferring layer 15adjoining to the substrate 13 b.

[0116] The pattern transferring layer 15 is an extremely thin film so asto have the microscopic pattern 22. With respect to a material for thepattern transferring layer 15, it is selected out of a metal, its alloy(including composition such as oxide, nitride, carbide, sulfide andfluoride), and resin. Further, thickness of the material is chosen froma range of 5 nm to 0.020 mm approximately. A typical example of resin issuch as novolac photosensitive resin and polyhydroxy styrenephotosensitive resin, which can be developed by alkali.

[0117] The information recording medium 4 of the fourth embodiment isevaluated for cross erase by the same manner as that of the firstembodiment and an identical result with the first embodiment isobtained.

[0118] Consequently, an identical effect with the information recordingmedium 1 according to the first embodiment can be obtained by theinformation recording medium 4 according to the fourth embodiment of thepresent invention.

[0119] It is apparent that each component of the information recordingmediums 1 through 4 shown in FIGS. 3 through 7 respectively can bereplaced with each other or combined as far as a reproductioncharacteristic is not deteriorated. For example, by preparing twomediums out of the information recording mediums 1 through 4, they canbe adhered together with facing each substrate 13, 13 a or 13 b(hereinafter generically referred to as “substrate 13”) towards eachother. Further, another set of the recording layer 12 and the lighttransmission layer 11 or 11 a (hereinafter generically referred to as“light transmission layer 11”) can be laminated on the lighttransmission layer 11 of the information recording mediums 1 through 4.By constituting as mentioned above, a recording capacity of theinformation recording medium 1 through 4 can be increased approximatelytwice.

[0120] Furthermore, although not shown in any drawings, an antistaticlayer commonly known can be formed on the surface of light transmissionlayer 11 opposite to the recording layer 12 in order to decrease dustadhering to the surface of the light transmission layer 11.

[0121] A hard coat layer or a lubricative layer (either one is notshown) can be formed on the surface of the light transmission layer 11opposite to the recording layer 12 for a purpose of reducing anaffection caused by an accidental collision of an objective lens, whichconstitutes a pickup of reproduction apparatus such as shown in FIG. 15,with the light transmission layer 11.

[0122] With respect to a material for such a hard coat layer, an actualmaterial having a light transparency of more than 70% for a light beamhaving a wavelength λ is as follows: thermosetting resin, various energyray curable resin (such as UV ray curable resin, visible light curableresin and electron beam curable resin), moisture curable resin, pluralliquid mixture curable resin and solvent containing thermoplastic resin.

[0123] The hard coat layer is desirable to exceed a certain value of the“scratch test by pencil” regulated by the Japanese Industrial Standard(JIS) K5400 in consideration of abrasion resistance of the lighttransmission layer 11. In consideration of that a hardest material ofthe objective lens is glass, a value of the “scratch test by pencil” forthe hard coat layer is most preferable to be more than the “H” grade. Ifthe test value is less than the “H” grade, dust caused by scraping thehard coat layer is remarkably generated. Consequently, an error rate isdeteriorated abruptly.

[0124] Further, a thickness of the hard coat layer is desirable to bemore than 0.001 mm in consideration of shock resistance, more desirableto be less than 0.01 mm in consideration of warp of an informationrecording medium in total. With respect to a coating method of the hardcoat layer, such a method as spin coat, splay, dip, blade coat, rollcoat, knife coating, screen printing and offset printing can be used.

[0125] With respect to other materials for the hard coat layer, anelement having a light transparency of more than 70% for a light beamhaving a wavelength λ and having a value of the “scratch test by pencil”of more than the “H” grade such as carbon, molybdenum and silicon, andtheir alloy (including composition such as oxide, nitride, carbide,sulfide and fluoride) can be used (its film thickness is within a rangeof 1 to 1000 nm). With respect to a forming method of the hard coatlayer, such methods as vacuum deposition of resister heating type orelectron beam type, direct current sputtering, high frequencysputtering, reactive sputtering, ion beam sputtering, ion plating andchemical vapor deposition (CVD) can be used.

[0126] With respect to an actual material for the lubricative layer,lubricant of which surface energy is adjusted by modifying hydrocarbonmacromolecule with silicon and fluorine can be used. Further, athickness of the lubricative layer is desirable to be within a range of0.1 to 10 nm approximately. With respect to a coating method of thelubricative layer, such a method as spin coat, splay, dip, blade coat,roll coat, knife coating, screen printing and offset printing can beused.

[0127] A label printing can be performed on the surface of the substrate13 although not shown in any drawings. Various energy ray curable resinscontaining pigment and dye (such as UV ray curable resin, visible lightcurable resin and electron beam curable resin) can be used suitably forthe label printing. A thickness of the label printing is preferable tobe more than 0.001 mm in consideration of visibility of the printing,more preferable to be less than 0.05 mm in consideration of warp of theinformation recording mediums 1 through 4 in total. With respect to aprinting method, such a method as screen printing and offset printingcan be used.

[0128] In order to improve easier loading of the information recordingmediums 1 through 4 into a reproducing apparatus and protectivenessbased on handling them, a constitution containing the informationrecording medium in a cartridge can be considered.

[0129] Further, in a case that the information recording mediums 1through 4 are in a disc shape, its dimensions are not limited. Varioussizes, for example, 20 to 400 mm in diameter can be acceptable, in anydiameter such as 32, 41, 51, 60, 65, 80, 88, 120, 130, 200, 300 and 356can also be acceptable.

[0130] In order to improve a recording characteristic and reproductioncharacteristic, the recording layer 12 can be composed of a plurality ofthin film materials. Such a recording layer composed of a plurality ofthin film materials will be detailed in the following embodiment.

[0131] [Fifth Embodiment]

[0132] With referring to FIG. 8, an information recording medium ofwhich recording layer is composed of four layers of thin film materialsaccording to a fifth embodiment of the present invention is explained.

[0133]FIG. 8 is a cross sectional view in partially enlarged of aninformation recording medium according to a fifth embodiment of thepresent invention.

[0134] In FIG. 8, a same composition as that of the first embodimentshown in FIG. 3 is indicated by a same sign as that of the firstembodiment and its explanation is omitted.

[0135] As shown in FIG. 8, an information recording medium 5 is composedof a reflective layer 121, a first protective layer 122, a recordinglayer 123, a second reflective layer 124 and a light transmission layer11, which are laminated on a substrate 13 having a microscopic pattern20 in order.

[0136] With respect to a material of the reflective layer 121, there isprovided a metal having a light reflectiveness such as Al, Au and Ag, analloy containing the metal as a main component and an additive elementsuch as more than one kind of metal or semiconductor and a mixture of ametal such as Al, Au and Ag with a metal compound such as metal nitride,metal oxide and metal chalcogenide. A metal such as Al, Au and Ag and analloy containing the metal as a main component are high inreflectiveness and thermal conductivity. Therefore, such a metal andalloy are preferable to be used.

[0137] Further, the reflective layer 121 has a role of optimizingthermal conduction while recording onto the recording layer 123.Therefore, it can be called a heat sink layer.

[0138] With respect to the alloy mentioned above, there is provided analloy of adding at least one element out of Si, Mg, Cu, Pd, Ti, Cr, Hf,Ta, Nb, Mn, Zr and Rh as an additive element to Al or Ag within a rangeof more than 1 atomic % and less than 5 atomic % in total or anotheralloy of adding at least one element out of Cr, Ag, Cu, Pd, Pt and Ni toAu within a range of more than 1 atomic % and less than 20 atomic %.Particularly, the reflective layer 121 is desirable to be constituted byany of Al—Cr alloy, Al—Ti alloy, Al—Ta alloy, Al—Zr alloy, Al—Ti—Cralloy or Al—Si-Mn alloy, which contains Al as a main component and anadditive element controlled within a range of more than 0.5 atomic % andnot more than 3 atomic % in total, because they are excellent incorrosion resistance and improve repetition ability.

[0139] With respect to an additive element, adding a metal or asemiconductor is more preferable than a metal alone, because acrystalline particle becomes smaller and a noise level decreases whenreproducing. Further, adding an additive is better so as to improvestability in an ambience of high temperature and high humidity.

[0140] Such an additive is an alloy such as Al—Ti, Al—Cr, Al—Zr, Al—Si,Ag—Pd—Cu and Ag—Rh—Cu. In a case of using a blue semiconductor laserhaving a wavelength of approximately 400 nm, using an alloy such asAl-system and Ag-system can obtain higher reflectivity. With respect toa thickness of the reflective layer 121, it is more than 10 nm and lessthan 300 nm.

[0141] The film thickness of the reflective layer 121 varies by athermal conductivity of a metal or an alloy constituting the reflectivelayer 121. In a case of an Al—Cr alloy, for example, thermalconductivity decreases in response to increasing content of Cr.Therefore, it does not conform to a recording strategy unless the filmthickness of reflective layer 121 is thickened. In a case of increasingcontent of Cr, the recording layer 123 becomes easy to be heated andhard to be cooled, that is so called, to be a gradually coolingstructure. In order to control forming a record mark by the recordingstrategy, some idea such as shortening a head pulse, shorteningmulti-pulse or extending a cooling pulse is required.

[0142] If a thickness of the reflective layer 121 exceeds 50 nm, thereflective layer 121 does not change optically and does not affect avalue of reflectivity. However, affection to a cooling speed becomeslarger. Since it takes more time to manufacture the thicker reflectionlayer 121 having a thickness of more than 300 nm, the film thickness ofreflection layer 121 must be controlled, if possible, by using amaterial having a higher thermal conductivity.

[0143] If the reflective layer 121 is divided into two layers or more, anoise level can be reduced when reproducing the information recordingmedium 5. Such a recording layer is formed, for example, as follows:

[0144] By using a single disc sputtering system, which forms each filmon each layer in a plurality of vacuum chambers, in a case of formingthe reflective layer 121 having a thickness of 150 nm in total bytransporting the substrate 13 one by one, a first reflective layer isformed in a first vacuum chamber at a filming speed of 2 nm/s, and thensecond and third reflective layers are formed by second and third vacuumchambers respectively at a filming speed of 6.5 nm/s. Consequently,discs can be filmed one after another in a short period of time as longas 10 seconds. A crystalline particle can be made finer by changing afilming speed, so that a noise level can be reduced when reproducing theinformation recording medium 5.

[0145] The first protective layer 122 and the second protective layer124 have an effect of protecting the substrate 13 and the recordinglayer 123 from excessive heat, preventing the substrate 13 and therecording layer 123 from deformation by the heat and preventing arecording characteristic from being deteriorated. Consequently, thefirst and second protective layers 122 and 124 have an effect ofimproving a signal contrast by an optical interference effect whilereproducing.

[0146] These protective layers 122 and 124 are transparent at awavelength of a light beam for recording and reproducing and itsrefractive index “n” is within a range of 1.9≦n≦2.5.

[0147] The first protective layer 122 and the second protective layer124 are not required to be a same material and composition. It isacceptable to be constituted by different materials. A thickness of thesecond protective layer 122 decides a wavelength exhibiting a minimumvalue of spectral reflectance.

[0148] Further, the first protective layer 122 and the second protectivelayer 124 have a further effect of activating crystallization of arecording layer and increasing an erase ratio. With respect to amaterial of these first and second protective layers 122 and 124, thereis existed an inorganic thin film such as ZnS, SiO₂, silicon nitride andaluminium oxide.

[0149] Particularly, a thin film of oxidized metal or semiconductor suchas Si, Ge, Al, Ti, Zr and Ta, a thin film of nitride metal orsemiconductor such as Si, Ge and Al, a thin film of carbide metal orsemiconductor such as Ti, Zr, Hf and Si, a thin film of sulfide metal orsemiconductor such as ZnS, In₂S₃, TaS₄ and GeS₂ and a film of a mixturecontaining more than two compounds out of the above-mentioned compoundssuch as oxide, nitride, carbide and sulfide are desirable for the firstand second protective layers 122 and 124 because they are high in heatresistance and chemically stable.

[0150] Furthermore, with respect to a material of the first and secondprotective layers 122 and 124, it is desirable that the material doesnot diffuse into the recording layer 121. These compounds of oxide,sulfide, nitride and carbide are not necessary to be a stoichiometricalcomposition. Controlling a composition and using them by mixing are alsoeffective for controlling a refractive index. By changing a contentamount of oxygen, sulfur, nitrogen and carbon, a refractive index “n” iscontrolled. If a content amount of them increases, a refractive indexdecreases.

[0151] A mixture film of ZnS and SiO₂ is particularly desirable for amaterial of the first and second protective layers 122 and 124, becauserecording sensitivity and C/N (carrier to noise ratio) are hard to bedeteriorated by a plurality of repetition of recording and reproducing.A thickness of the first protective layer 122 and the second protectivelayer 124 are within a range of 10 to 500 nm respectively. The thicknessof the first protective layer 122 is desirable to be within a range of10 to 50 nm so as to be excellent in a recording characteristic such asC/N and erase ratio and to be rewritable stably a plurality of times.

[0152] If a thickness of the first protective layer 122 is thinner, areflectivity increases and a recording sensitivity decreases. Further, aspace between the first protective layer 122 and the reflective layer121 becomes narrower and the first protective layer 122 becomes a rapidcooling construction, so that a relatively large recording power isnecessary to forming a record mark. On the contrary, if the thickness offirst protective layer 122 becomes thicker, the space between the firstprotective layer 122 and the reflective layer 121 becomes wider and thefirst protective layer 122 becomes a gradually cooling structure.Consequently, a rewriting performance is deteriorated and a repetitionnumber of overwriting decreases.

[0153] A film thickness of the first protective layer 122 is thinnerthan that of the second protective layer 124, the first protective layer122 becomes a rapid cooling structure. In order to relief thermaldamage, a film thickness of the first protective layer 122 is desirableto be within a range of 2 to 50 nm. Further, it is preferable that afilming speed of the first protective layer 122 must be slower than thatof the second protective layer 124. Consequently, increasing of jitterby rewriting is suppressed and a number of rewriting increases.

[0154] With respect to a material of the recording layer 123, the samephase change material as that of the recording layer 12 of the firstthrough fourth embodiment can be used. A film thickness of the recordinglayer 123 is within a range of 5 to 100 nm, desirably, 10 to 30 nm inorder to increase a reproduced signal.

[0155] The same material as the first protective layer 122 is used forthe second protective layer 124. A thickness of the second protectivelayer 124 is within a range of 10 to 200 nm. The thickness of the secondprotective layer 124 is desirable to be within a range of 40 to 150 nmin order to increase a reproduced signal although an optimum filmthickness varies by a wavelength of a light source to be used. In a casethat a laser beam for recording is blue (having a wavelength of 400 nmapproximately), a modulated amplitude can be increased if the filmthickness of the second protective layer 124 is set to be 40 to 60 nm.

[0156] As mentioned above, according to an aspect of the fifthembodiment of the present invention, recording and reproducingcharacteristics of the information recording medium 5 can be improved inaddition to the effects according to the first through fourthembodiment.

[0157] The laminated structure of the protection layers can be appliedto the information recording mediums 2 though 4 as well as theinformation recording medium 1. Further, in order to improve therecording and reproducing characteristics more, an auxiliary thin filmcan be formed on each layer or between layers.

[0158] As mentioned above, according to the first through fifthembodiment of the present invention, recording in either the groovesection G or the land section L can decrease the cross erase.

[0159] Furthermore, for a point of view of signal quality, theinformation recording medium 5 of the present invention is studied thateither of the groove section G and the land section L is more suitableto be recorded. Consequently, it is found that an error rate is low anda rewriting characteristic is excellent when recorded in the landsection L.

[0160] In consideration of the allocation of the land section L, whichis allocated in a closer side to the light transmission layer 11 thanthe groove section G, and a reproduction light, which enters in from thelight transmission layer 11, it is understood that the area of the landsection L has a nature of ideally recording a record mark in a uniformshape as well as can easily accumulate heat in a material of the landsection L and becomes higher sensitivity. (On the other hand, in a caseof recording in the groove section G, heat is easily radiated.Therefore, it is understood that an ideal recording can hardly beperformed.)

[0161] A modulation pattern for embedding an auxiliary information (subinformation) such as address data in analog or digital with respect tothe information recording medium 1 according to the present invention isdetailed next.

[0162] The auxiliary information (sub information) is recorded in a formof wobbled pattern by the method of amplitude modulation (AM), frequencymodulation (FM) or phase modulation (PM) as mentioned above. In otherwords, the auxiliary information is directly recorded (on the substrate13 or the light transmission layer 11 and formed in a shape of groove)as a wobbling pattern. Therefore, the auxiliary information is apermanent information being disabled to rewrite.

[0163] In a case that the information recording medium 1 is in a discshape, the auxiliary information is recorded in a wobbling form withrespect to a groove, which extends to the tangential direction of thedisc. Consequently, the wobbling direction is the radial direction ofthe disc.

[0164] An address data, which is one of the auxiliary information (subinformation) to be recorded in the present invention, is a date selectedout of an absolute address, which is assigned to whole the informationrecording medium 1, a relative address, which is assigned to a partialarea, a track number, a sector number, a frame umber, a field number, atime information and a error correction code. It is a data, which isconverted from a data described in the decimal notation or thehexadecimal notation, for example, to the binary notation (including theBCD code and gray code).

[0165] Further, an auxiliary information other than an address data canalso be handled. Such an auxiliary information is a specific code data,which is at least selected out from information and data such as, forexample, a type of information recording medium, a size of theinformation recording medium, an ideal recording capacity of theinformation recording medium, an ideal linear recording density of theinformation recording medium, an ideal linear velocity of theinformation recording medium, a track pitch of the information recordingmedium, a recording strategy information, a reproducing powerinformation, a manufacturer information, a manufacturing number, a lotnumber, a control number, a copyright related information, a key forproducing a cipher, a deciphering key, a ciphered data, a recordingpermission code, a recording refusal code, a reproduction permissioncode and a reproduction refusal code. It is also acceptable that thesedata are accompanied by an error correction code.

[0166] In order to simplify explanation, hereinafter it is explainedwith assuming that an auxiliary information (sub information) is anaddress.

[0167]FIG. 9 is an enlarged plan view of an address 250 recorded by theamplitude modulation (AM) method in an information recording mediumaccording to the present invention. The address 250 is recorded in shapepartially or totally onto either the groove section G or the landsection L, which constitutes the microscopic pattern 20. In the AMmethod, a data “1” or “0” is recorded in accordance with an amplitudewhether or not it is existed. In a case of FIG. 9, a data “1” isrecorded as a section 251 having amplitude and another data “0” asanother section 252 having no amplitude.

[0168] In a case that an address “10110”, for example, is recorded, asshown in FIG. 9, the section 251, the other section 252, the section251, the section 251 and the other section 252 are sequentially recordedin shape. Such a recording method of data in response to amplitudewhether or not it is existed is advantageous to be able to demodulateeven in a deteriorated C/N circumstance because the AM method is asimple signal format system. Particularly, affection of crosstalk froman adjacent track can be minimized. Consequently, the AM method is aneffective address recording method for the information recording medium1 according to the present invention reducing the pitch P more than thespot diameter S of a light beam for reproduction.

[0169] Each duration of the section 251 and the other section 252 isacceptable to be either the same duration or not. However, the durationis desirable to be the same in order to make an error rate ofdemodulation the best. Further, a number of waves constituting thesection 251 is not limited to one specific number. The number must beplural in order to eliminate a readout error, and a number being notredundant is suitable for the number of waves so as not to decrease arecording density of address recording. From the point of view of theabove-mentioned circumstances, the number of waves is desirable to be 2to 10 approximately. Furthermore, each amplitude of a plurality of thesections 251 can be different from each other. However, it is desirableto be the same in consideration of easier setting of a slice level whendemodulating.

[0170] In a case that an extra area recorded with a single frequency forclock other than the address 250 is provided, it is not concernedwhether or not the single frequency is the same as a frequency of thesection 251. However, if it is the same frequency, a physical lengthused for extracting clock can be extended slightly. Consequently, thesame frequency is advantageous for stable extraction of clock to beeasier.

[0171]FIG. 10 is an enlarged plan view of an address 300 recorded in aninformation recording medium according to the present invention by thefrequency modulation (FM) method. The address 300 is recorded in shapepartially or totally onto either the groove section G or the landsection L, which constitutes the microscopic pattern 20. In the FMmethod, a data “1” or “0” is recorded in accordance with a frequencywhether it is higher or lower. In a case of FIG. 10, a data “1” isrecorded as a section 301 having a higher frequency and another data “0”as another section 302 having a lower frequency.

[0172] In a case that an address “10110”, for example, is recorded, asshown in FIG. 10, the section 301, the other section 302, the section301, the section 301 and the other section 302 are sequentially recordedin shape.

[0173] Such a recording method of data in response to a frequencywhether it is higher or lower is advantageous to be able to demodulateby a simplified circuitry. Particularly, as shown in FIG. 10, byselecting a proper phase, which is suitable for two waves to beconnected continuously at a point where their frequencies change over, areproduction envelope becomes approximately constant and stable addressextraction can be realized. Each duration of the section 301 and theother section 302 is acceptable to be either the same duration or not.However, the duration is desirable to be the same in order to make anerror rate of demodulation the best.

[0174] A number of waves constituting the section 301 and the othersection 302 is arbitrary. Further, each amplitude of the section 301 andthe other section 302 can be different from each other. However, it isdesirable to be the same amplitude in consideration of easierdemodulation. Furthermore, selecting a frequency of the section 301 andthe other section 302 is arbitrary. However, it is desirable to assignthe two frequencies of which phase difference is within a range of ±π/12to ±π/0.75. Particularly, in a case that a frequency ratio (of higherfrequency to lower frequency) is assigned to be 1.5 as shown in FIG. 10,the two frequencies are related to that a phase of each wave is shiftedby −π/2.5 and +π/2.5 respectively. These two frequencies can beexpressed in integral multiples (triple and twice hereat) of a singlefrequency (0.5 hereat). Consequently, there is existed an advantage ofconstituting a demodulation circuit simply. Moreover, a demodulation canbe performed by the synchronous detection method, so that an error ratecan be reduced remarkably.

[0175] In a case that a frequency ratio (of higher frequency to lowerfrequency) is assigned to be 1.28 as another example, the twofrequencies are related to such that a phase of each wave is shifted by−π/4 and +π/4 respectively. Consequently, in this case, a demodulationcan also be performed by the synchronous detection method, so that anerror rate can be reduced remarkably.

[0176] In a case that an extra area recorded with a single frequency forclock other than the address 300 is provided, it is acceptable that thesingle frequency and frequencies of the section 301 and the othersection 302 are different frequencies from each other. However, aphysical length used for extracting clock can be extended slightly ifeither frequency of the section 301 and the other section 302 is thesame as that of the single frequency. Consequently, the same frequencyis advantageous for stable extraction of clock to be easier.

[0177]FIG. 11 is an enlarged plan view of a first phase modulation (PM)address 400 recorded in an information recording medium according to thepresent invention. The first PM address 400 is recorded in shapepartially or totally onto either the groove section G or the landsection L, which constitutes the microscopic pattern 20. In the PMmethod, a data “1” or “0” is recorded in accordance with a phasedifference. In the case of FIG. 11, a data “1” is recorded as a “sine 0”section 401 and another data “0” as a “sine π” section 402. Further, ina case that an address “10110”, for example, is recorded, as shown inFIG. 11, the “sine 0” section 401, the “sine π” section 402, the “sine0” section 401, the “sine 0” section 401 and the “sine π” section 402are sequentially recorded in shape.

[0178] Such a recording method of data in response to a phase differenceis advantageous to be able to reproduce by demodulating by thesynchronous detection method even in a deteriorated C/N circumstance.Each duration of the “sine 0” section 401 and the “sine π” section 402is acceptable to be either the same duration or not. However, theduration is desirable to be the same in order to make an error rate ofdemodulation the best. Further, each amplitude of the “sine 0” section401 and the “sine π” section 402 can be different from each other.However, it is desirable to be the same amplitude in consideration ofeasier demodulation.

[0179] Furthermore, a phase difference between two data is assigned tobe π and the two data are recorded in two values of “0” and π. However,it is not limited to “0” and π. For example, with assigning that a phasedifference is π/2, it is acceptable to be recorded in four values of−3π/4, −π/4, +π/4 and +3π/4.

[0180] In a case that an extra area recorded with a single frequency forclock other than the first PM address 400 is provided, it is acceptablethat the single frequency and a frequency of either the “sine 0” section401 or the “sine π” section 402 are different from each other. However,a physical length used for extracting clock can be extended slightly ifthese frequencies coincide with each other. Consequently, the samefrequency is advantageous for stable extraction of clock to be easier.

[0181] Further, the single frequency for clock can be recorded bysuperimposing on the first PM address 400. In other words, an integralmultiples (including one) or one over integral multiples of frequencycan be superimposed on a PM address. In a case of superimposing a clockfrequency as mentioned above, frequencies can be separated by using acommonly known band pass filter. However, it is desirable that frequencydifference between the first PM address 400 and a clock frequency islarger. For example, with assuming that a frequency of the first PMaddress 400 is “1” and a clock frequency is ½, these frequencies areideally separated and both address and clock can be extracted stably.

[0182]FIG. 12 is an enlarged plan view of a second phase modulation (PM)address 450 recorded by the PM method. A shape is recorded in either thegroove section G or the land section L constituting the microscopicpattern 20. In this method, a wave is regarded as an asymmetrical shapeof rising and falling. Phase difference is expressed by controlling eachwave individually. That is, in a case of FIG. 12, the data “1” isrecorded as a section 451 of which a wave rises gradually and fallsrapidly (hereinafter referred to as a rapidly falling section 451), andthe data “0” as a section 452, which rises rapidly and falls gradually(hereinafter referred to as a rapidly rising section 452).

[0183] In a case that an address “10110”, for example, is recorded, asshown in FIG. 12, the rapidly falling section 451, the rapidly risingsection 452, the rapidly falling section 451, the rapidly fallingsection 451 and the rapidly rising section 452 are sequentially recordedin shape.

[0184] Such a recording method of data in response to a phase differenceis advantageous to be able to demodulate by inputting into a wide-bandfilter and extracting a differential component even in a deterioratedC/N circumstance. Each duration of the rapidly falling section 451 andthe rapidly rising section 452 is acceptable to be either the sameduration or not. However, the duration is desirable to be the same inorder to make an error rate of demodulation the best.

[0185] Each amplitude of the rapidly falling section 451 and the rapidlyrising section 452 can be different from each other. However, it isdesirable to be the same amplitude in consideration of easierdemodulation. Further, in a case that an extra area recorded with asingle frequency for clock other than the second PM address 450 isprovided, it is acceptable that the single frequency and a frequency ofeither the rapidly falling section 451 or the rapidly rising section 452are different from each other. However, a physical length used forextracting clock can be extended slightly if these frequencies coincidewith each other. Consequently, the same frequency is advantageous forstable extraction of clock to be easier.

[0186] In the explanation of recording methods by the AM, FM and PMheretofore, it is explained by using the recording method, which recordsan address data itself as a shape of wobbling groove directly. Further,a fundamental wave of wobbling groove is on the assumption of asinusoidal shape. However, the shape according to the present inventionis not limited to the sinusoidal shape. For example, it is apparent thatthe same effect is recognized by using a cosine shape for thefundamental wave of wobbling groove.

[0187] An address data can also be recorded in multiple recording andtime sharing recording by a different modulation method. For example, itcan be recorded by synthesizing different methods such as AM+FM, AM+PMand FM+PM. Further, it can be recorded by a time sharing recordingmethod such as recording for a period of time by the AM and for anotherperiod of time by the FM, recording for a period of time by the AM andfor another period of time by the PM or recording for a period of timeby the FM and for another period of time by the PM. As mentioned above,it is also acceptable that a single frequency area for extracting aclock is recorded for a certain period of time being different from theperiod for recording the address data as a time sharing recording methodin addition to the time sharing recording of the address data.

[0188] With respect to an amplitude of wobbling groove, by assigning adeflection amplitude by wobbling s as to be less than the pitch P,excellent reproduction of address can be realized. Actually, an address,which does not contact with an adjacent track physically, can berecorded by assigning amplitude by wobbling to be less than the pitch P,so that crosstalk caused by recording can be eliminated.

[0189] By attempting such that writing a random data by the phase changerecording in a groove, which is recorded with an address with assigningsuch a wobble amplitude to be less than the pitch P, and thenreproducing the address by the push-pull method, it is found that awobble amplitude (peak to peak) is more than 2% of the spot diameter Sof light beam for reproduction as a limit possible to detect the addresssignal. Further, it is found that a random data caused by the phasechange recording is remarkably superimposed as a noise and an addresserror rate increases suddenly with respect to a groove formed such thatthe wobble amplitude is less than 2% of the spot diameter S.

[0190] On the other hand, in a case that the wobble amplitude is morethan 9% of the spot diameter S, crosstalk from an adjacent track isremarkably superimposed on a push-pull signal and an address error rateincreases suddenly. Consequently, a wobble amplitude is essential to beless than the pitch P. Further, it is most suitable for the wobbleamplitude to be within a range of 2 to 9% of the spot diameter S oflight beam for reproduction.

[0191] In the present invention, the recording method is not limited tothe direct recording. In a case of recording a long array of addressdata, it is possible that a plurality of “0”s or a plurality of “1”s isarranged sequentially and a direct current component is generated in thedata by the direct recording method.

[0192] In order to eliminate such possibility, it is acceptable toperform a method such that the data is previously modulated by thebase-band modulation and recorded. In other words, the method is thatreplace “0” and “1” with another code previously and reduce a sequenceof “0”s and “1”s to a certain number or less. With respect to such amethod, the method such as Manchester code, PE (phase encoding)modulation, MFM (modified frequency modulation), M2 (Miller squared)modulation, NRZI (non return to zero inverted) modulation, NRZ (nonreturn to zero) modulation, RZ (return to zero) modulation anddifferential modulation can be used alone or by combining some of them.

[0193]FIG. 13 is a table exhibiting a change of fundamental data ofbefore and after a base-band modulation.

[0194] With respect to a base-band modulation method, which is mostsuitable for the information recording medium 1 of the presentinvention, it is the Manchester code (biphase modulation) method. TheManchester code method is a method of applying 2 bits to each one bit ofdata to be recorded as shown in FIG. 13. That is, “00” or “11” isassigned to a data “0” to be recorded, and “01” or “10” to a data “1”.Further, an inverted code of inverting a last code of preceding data isessentially applied to a head code of succeeding data when arranging thesucceeding data after the preceding data.

[0195]FIG. 14 is a table of definite example exhibiting a change of dataarray of before and after a base-band modulation. As shown in FIG. 14,an address data “100001” is assigned to be a code array of“010011001101”. The original address data contains a sequence of four“0”s. Further, the original address data is an asymmetrical data that anappearing probability of “0” is twice that of “1”. If such anasymmetrical data is modulated, a sequence of “0” or “1” is twomaximally and the original data is converted into a symmetrical datahaving equal appearing probability of “0” and “1”. As mentioned above,the base-band modulation, which restricts a sequence of same bits withina certain quantity, is effective to increase stability of reading out adata. Consequently, the base-band modulation method is suitable forpre-treatment for a long address data.

[0196] Further, there is existed another method of highly analyzing anaddress data and recording it in dispersion. For example, in combinationwith a dummy data “10”, it is a recording method such that an addressdata is recorded as a data array of “10X”, wherein “X” is either “0” or“1”, and the data array is allocated at every certain interval. If the“X” is extracted by using the dummy data “10” as a data trigger, theoriginal data can be restored. This method is effective for a format,which can be read a data array to be treated with taking a long periodof time.

[0197] With respect to another example of the dispersion recording,there is existed a method such that a first specific data pattern(“101”, for example), which is easy to read, is allocated (recorded) atevery certain interval, and then a second specific data pattern (“1111”,for example), which is easy to read, is allocated between the firstspecific data patterns. A position of allocating the second specificpattern is advanced to a predetermined distance (time) with respect tothe first specific pattern. The second specific pattern is recorded as adata “1” if the other second specific patter is existed at the position.If the other second specific patter is not existed at the position, adata “0” is recorded there.

[0198] When reading a data, with paying attention to a predeterminedposition, the second specific pattern can be read out whether or not itis existed. By following such a method, a recorded address data can beread out. Further, by assigning two positions of allocating the secondspecific pattern previously, which are advanced to a predetermineddistance (time) with respect to the first specific pattern, a data “1”or “0” can be recorded at either position, where the second specificpatter exists.

[0199] The dispersion recording method by using a difference in distancebetween the first specific pattern and the second specific pattern isexplained above. However, in a case that a pattern having extremely highaccuracy in readout can be provided for a specific pattern, the firstspecific pattern and the second specific pattern are acceptable to beidentical with each other. With respect to a specific pattern recordedby a certain period of time interval, it is acceptable that the data “1”and the data “0” are identified by extracting another specific patternhaving a shorter time interval than the specific pattern and measuringthe time interval.

[0200] The recording of an auxiliary information (sub information)composed of an address information and a specific code data by wobblinggroove is explained hereinbefore. Although it is repeated once again,the recording explained herein is recording in shape by wobbling of agroove (the groove section G or the land section L) not recording ontothe recording layer 12. The recording in shape by wobbling groove of theauxiliary information and the clock information (single frequency forextracting clock) mentioned above is a permanent information, which cannot be altered and is high in concealment. Such recording can beperformed by applying a method of forming a record accompanying shapechange on the substrate 13 or the light transmission layer 11.

[0201] The forming a record is realized by using a stamper recorded withwobbling groove. The stamper itself is manufactured by the so-calledmastering method for forming a wobbling pattern by using an energy ray.

[0202] In the meantime, as mentioned above, recording onto the recordinglayer 12 (phase change recording, for example) is applied to the groovesection G or the land section L. When recording onto the recording layer12, the recording is performed with referring to an auxiliaryinformation and a clock information recorded by wobbling groove (forexample, recording with reading an address). Therefore, a track appliedfor recording must coincide with another track recorded in shape with anauxiliary information and a clock information.

[0203] For example, if a track applied for recording is the land sectionL, another track recorded in shape with the auxiliary information andthe clock information must be the land section L. If they are differentfrom each other, the auxiliary and clock information are extracted withmixing with 50% each of information recorded in adjacent two tracks, sothat accurate auxiliary information and clock information can not beextracted, although recording onto the recording layer 12 can bephysically performed without any problem.

[0204] In another case, if a track applied for recording is the landsection L and another track recorded in shape with an auxiliaryinformation and a clock information is the groove section G, recordingonto the land section L in the recording layer 12 is naturallyperformed. However, if the auxiliary information such as an address andthe clock information are extracted while recording, an informationrecorded in two adjacent groove sections G, which sandwich the landsection L, is read out. Consequently, the auxiliary and clockinformation are extracted with mixing with 50% each of auxiliaryinformation and clock information recorded in two adjacent groovesections G different from the original groove section G.

[0205] It is impossible to separate the mixed two information, so thatrecording onto a track intended to be recorded can not be performed.Accordingly, a track applied for recording is necessary to coincide withanother track recorded in shape with an auxiliary information and aclock information.

[0206] As mentioned above, recording onto the recording layer 12 issuitable to record on the land section L in a sense of decreasing anerror rate. Therefore, it is most desirable that a track supplied forrecording is the land section L and another track recorded in grooveshape with an auxiliary information and a clock information is also theland section L.

[0207] With referring to FIG. 15, a first reproducing apparatus 40utilized for reproducing the information recording mediums 1 through 5is explained next.

[0208]FIG. 15 is a block diagram of a first reproducing apparatusaccording to the present invention.

[0209] In order to simplify an explanation, hereinafter the informationrecording medium 1 represents the information recording mediums 1through 5 generically.

[0210] As shown in FIG. 15, a first reproducing apparatus 40 is at leastcomposed of a pickup 50 for reading out reflected light from theinformation recording medium 1, a motor 51 for rotating the informationrecording medium 1, a servo device 52 for controlling to drive thepickup 50 and the motor 51, a turntable 53 for supporting theinformation recording medium 1, a demodulator 54 for demodulating aninformation signal read out by the pickup 50, an interface (I/F) 55 fortransmitting a signal demodulated by the demodulator 54 externally and acontroller 60 for controlling the first reproducing apparatus 40totally. The demodulator 54 is a digital converter, which restores a16-bit data to an original 8-bit data, in a case of the 8/16 modulation(Eight to Fifteen Modulation Plus: EFM Plus) method utilized in the DVDsystem, for example.

[0211] The turntable 53 and the information recording medium 1 areconnected with plugging a center hole Q of the information recordingmedium 1 with the turntable 53. Such a connection between the turntable53 and the information recording medium 1 can be either a fixedconnection or semi-fixed connection, which can load or release theinformation recording medium 1 freely. Further, the informationrecording medium 1 can be installed in a cartridge. With respect to acartridge, a commonly known cartridge having an opening and closingmechanism in the center can be used as it is.

[0212] The motor 51 is linked to the turntable 53, supports theinformation recording medium 1 through the turntable 53 and suppliesrelative motion for reproduction to the information recording medium 1.A signal output can be supplied to a not shown external output terminalor directly supplied to a not shown display device, audio equipment orprinting equipment.

[0213] The pickup 50 is further composed of a light emitting element 50a, which irradiates a light beam having a single wavelength λ within arange of 350 to 450 nm, desirably 400 to 435 nm, an objective lens 50 bhaving a numerical aperture NA within a range of 0.75 to 0.9 and a notshown photo detector, which receives a reflected light reflected by theinformation recording medium 1. Furthermore, the pickup 50 forms areproducing light 70 in conjunction with these components.

[0214] It is acceptable that the light emitting element 50 a is asemiconductor laser of gallium nitride system compound or a laser havinga second harmonic generating element.

[0215] The servo device 52 is indicated just one in FIG. 15. However, itcan be divided into two; one is a driving control servo for the pickup50 and the other is another driving control servo for the motor 51.

[0216] A commonly know equalizer and a PRML (partial response maximumlikelihood) decoding circuit, both are not shown, can be installed inthe demodulator 54. With respect to an equalizer (waveform equalizer),for example, a so-called neural net equalizer (such as disclosed in theJapanese Patent No. 2797035) in which a plurality of conversion systemshaving a nonlinear input-output characteristic is combined together withapplying individual variable weighting and constitutes a neural network,a so-called limit equalizer (such as disclosed in the Japanese PatentApplication Laid-open Publication No. 11-259985/1999) in which anamplitude level of reproduced signal is limited to a predetermined valueand forwarded to a filtering process, and a so-called error selectiontype equalizer (such as disclosed in the Japanese Patent ApplicationLaid-open Publication No. 2001-110146) in which an error between areproduced signal and an objective value for waveform equalization isobtained and a frequency of waveform equalizer is changed adaptively soas to minimize the error can be preferably used.

[0217] Further, in the commonly known PRML decoding circuit containing apredicted value controlling and equalization error calculating circuit,a so-called adaptive viterbi decoder (such as disclosed in the JapanesePatent Application Laid-open Publications No. 2000-228064 and No.2001-186027) in which a predicted value utilized for decoding viterbialgorithm is calculated and a frequency response is optimized so as tominimize an equalization error of waveform equalizer can be suitablyused.

[0218] Operations of the first reproducing apparatus 40 are explainednext.

[0219] The reproducing light 70 emitted form the light emitting element50 a of the pickup 50 is converged at the microscopic pattern 20 in theinformation recording medium 1. Actually, the reproducing light 70 isfocused on the microscopic pattern 20, which is allocated at a depth of0.07 to 0.12 mm equivalent to a thickness of the light transmissionlayer 11.

[0220] Succeedingly, tracking of the reproducing light 70 is performedto either one of the groove section G or the land section L. Thetracking is performed with choosing a predetermined side. However, asmentioned above, choosing the land section L is most desirable. Arecorded signal is read out by a light detector not shown with receivinga reflected light from the microscopic pattern 20.

[0221] The light detector is divided into 4 sections. A total sum signal(that is, Ia+Ib+Ic+Id) of output from all 4 sections of the lightdetector is transmitted to the demodulator 54, wherein each of Ia, Ib,Ic and Id corresponds to each output of a 4-division light detector fora DVD disc defined by the JIS Standard No. X6241: 1997. Reading out ofthe recorded signal is performed by reproducing the record mark Mrecorded in the groove section G or the land section L on themicroscopic pattern 20.

[0222] It is omitted in the above explanation that a focus error signalis necessary for focusing to be generated and a tracking error signal isnecessary for tracking to be generated. Such a focus error signal and atracking error signal are generated by a differential signal (that is,“(Ia−Ib)−(Ic−Id)”) of output from a 4-division light detector in theradial direction and transmitted to the servo device 52.

[0223] In accordance with control by the controller 60, in the servodevice 52, a focus servo signal and a tracking servo signal aregenerated from the received focus error signal and the tracking errorsignal and transmitted to the pickup 50. In the meantime, a rotary servosignal is generated in the servo device 52 and transmitted to the motor51.

[0224] Further, in the demodulator 54, the recorded signal isdemodulated and applied with error correction according to demand, andan obtained data stream is transmitted to the I/F 55. Finally, a signalis outputted externally in accordance with control by the controller 60.

[0225] As mentioned above, the information recording medium 1 and thefirst reproducing apparatus 40 according to the present invention aredesigned for coping with the reproducing light 70, which is produced bythe light emitting element 50 a having single wavelength λ within therange of 350 to 450 nm and the objective lens 50 b having the numericalaperture NA of 0.75 to 0.9. Therefore, the first reproducing apparatuscan preferably reproduce the information recording medium 1.

[0226] With respect to the light emitting element 50 a in the firstreproducing apparatus 40, it is defined that the light emitting element50 a can be a semiconductor laser of gallium nitride system compound ora laser having a second harmonic generating element. However, these twodifferent lasers have a characteristic laser noise respectively,particularly, in a case of a semiconductor laser of gallium nitridesystem compound, it is characterized by a higher noise level.

[0227] According to an actual measurement, an RIN (relative intensitynoise) of a laser having a second harmonic generating element is −134dB/Hz. The noise level is almost equivalent to that of a redsemiconductor laser (λ=650 nm approximately) utilized for a DVD disc.

[0228] On the other hand, in a case of a semiconductor laser of galliumnitride system compound, an RIN is −125 dB/Hz. The noise level is largerthan that of a laser having a second harmonic generating element by 9dB. The noise is added to a reproduced signal from the informationrecording medium 1 and a S/N of the reproduced signal is extremelydeteriorated. In other words, if a semiconductor laser of galliumnitride system compound is adopted for the first reproducing apparatus40, a signal characteristic is deteriorated. Therefore, it signifiesthat a designing guide obtained by a DVD disc can not be applied for thefirst reproducing apparatus 40 with shifting the designing guideproportionally. Consequently, in a case of the first reproducingapparatus 40 having a semiconductor laser of gallium nitride systemcompound, an information recording medium having a signal characteristicof compensating a deteriorated component is necessary to be provided inconsideration of being added with a noise inherent to a laser.

[0229] With respect to the information recording medium 5 shown in FIG.8 according to the fifth embodiment of the present invention, arelationship between modulated amplitude and error rate is examined bymanufacturing various kinds of mediums with varying material andthickness of the reflective layer 121, the first protective layer 122,the recording layer 123 and the second protective layer 124 and byreproducing the mediums by using the first reproducing apparatus 40,which is installed with a semiconductor laser of gallium nitride systemcompound (having a RIN of −125 dB/Hz) for the light emitting element 50a.

[0230] In addition thereto, recording on the information recordingmedium 5 is performed under a most ideal recording condition, whichdecreases an error rate maximally.

[0231] Reproduced modulated amplitude is also called an output ofreproduced signal. In a case of a phase change recording material, it isan index having correlation with reflectivity contrast between crystaland amorphous. In more accurately, a modulation signal so-called a (d,k) signal is recorded on the information recording medium 5. A recordingapparatus will be explained later.

[0232] A fixed length code and a variable length code can be applied fora (d, k) modulation signal. Such a (d, k) modulation as (2, 10)modulation in a fixed length code, (1, 7) modulation in a fixed lengthcode, (1, 9) modulation in a fixed length code, (2, 7) modulation invariable length code and (1, 7) modulation in the variable length codecan be suitably used.

[0233] Examples representing the (2, 10) modulation in a fixed lengthcode are the 8/15 modulation (such as disclosed in the Japanese PatentApplication Laid-open Publication No. 2000-286709), the 8/16 modulation(EFM plus) and the 8/17 modulation (EFM). Further, an examplerepresenting the (1, 7) modulation in the fixed length code is the “D1,7” modulation (such as disclosed in the Japanese Patent Application No.2001-80205 in the name of Victor company of Japan, Limited).Furthermore, an example representing the (1, 9) modulation in the fixedlength code is the “D4, 6” modulation (such as disclosed in the JapanesePatent Application Laid-open Publication No. 2000-332613). Moreover, anexample representing the (1, 7) modulation in the variable length codeis the 17PP modulation (such as disclosed in the Japanese PatentApplication Laid-open Publication No. 11-346154/1999).

[0234] Modulated amplitude is obtained from a signal having a maximallength used by a code by reproducing the information recording medium 5loaded flat (without declining) in the first reproducing apparatus 40and by connecting a reproduced signal in the DC system outputted fromthe pickup 50 to an oscilloscope.

[0235] In the case of the 8/16 modulation used for a DVD disc, forexample, the maximal length is 14T. By measuring an I14L and I14H asspecified by the specification (JIS Standard X6241: 1997), modulatedamplitude can be obtained by calculating (I14H−I14L)/I14H.

[0236] Further, an error rate is obtained by measuring a reproducedsignal obtained through the demodulator 54. A result of obtainingmodulated amplitude and an error rate is shown in FIG. 16.

[0237]FIG. 16 is a graph exhibiting a relation between modulatedamplitude and error rate.

[0238] As shown in FIG. 16, there is existed a definite correlationbetween modulated amplitude and error rate. It is apparent that an errorrate remarkably increases in accordance with decreasing modulatedamplitude. By assigning a practical error rate to 3×10⁻⁴ defined by aDVD disc or like, a necessary modulated amplitude is more than 0.34.

[0239] Further, the information recording medium 5 warps by temperaturechange or like in circumstances of utilization of the informationrecording medium 5. Therefore, with assuming that a declination ofapproximate 0.7 degree is possible to occur as a same situation as a DVDdisc, an error rate increases due to coma aberration, which is complexlyproduced by a wavelength λ within a range of 350 to 450 nm, an NA withina range of 0.75 to 0.9 and a thickness of the light transmission layer11 within a range of 0.07 to 0.12 mm.

[0240] By the result of measurement, it is found that the error rate of3×10⁻⁴ at the declination of 0.7 degree is equivalent to an error rateof 0.7×10⁻⁴ at the declination of zero degree. In other words, the errorrate of 0.7×10⁻⁴ is essential in consideration of a possible declinationwhen using the information recording medium 5 practically. Accordingly,it is understood that practical modulated amplitude is more than 0.4.

[0241] As mentioned above, in the case that a semiconductor laser ofgallium nitride system compound is used for a light emitting element, anerror rate can be reduced to a practical level as low as that of the DVDdisc specification if modulated amplitude of the information recordingmedium 5 is assigned to be more than 0.4 in consideration of a noisebeing added to a reproduced signal. Further, it is found by experimentsthat a correlation between modulated amplitude and error rate such asshown in FIG. 16 can be obtained as a similar result by applying any ofthe modulation methods mentioned above.

[0242] A maximum mark length can vary by a modulation method. However, asignal output almost saturates at more than 6T by these modulationmethods and converges to a certain value. Consequently, modulatedamplitude obtained by recording the information recording medium 1 bythe 17PP modulation method, for example, and another modulated amplitudeobtained by the 8/16 modulation method become a same value as eachother. Modulated amplitude by the (1, 7) system modulation method suchas the “D1, 7” modulation method and the 17PP modulation method can beobtained by (I8H−I8L)/I8H because the maximum mark length becomes 8T.

[0243] Hereinafter, information recording mediums according toembodiments 1 through 5 are more actually explained. In additionthereto, samples of information recording mediums according tocomparative examples 1 through 3 are also manufactured in order tocompare.

[0244] [Embodiment 1]

[0245] Polycarbonate having a thickness of 1.1 mm is used for asubstrate 13 of a phase change type information recording medium 5.Further, the information recording medium 5 is manufactured by usingmaterials such as AgPdCu for a reflective layer 121, ZnSSiO₂ for a firstprotective layer 122, AgInSbTe for a recording layer 123, ZnSSiO₂ for asecond protective layer 124 and polycarbonate having a thickness of 0.10mm for a light transmission layer 11. An address data is recorded in awobbling shape on a land section L of the information recording medium 5by the frequency modulation method, wherein a phase having a phasedifference of ±π/2.5 is selected so as for a wave to be continuous at apoint of changing a frequency. Furthermore, the information recordingmedium 5 is designed with assuming that it is recorded by using a lightbeam having a wavelength λ of 405 nm and an objective lens having anumerical aperture NA of 0.85, and a pitch P between land sections L is0.32 μm.

[0246] The information recording medium 5 is loaded into a recordingapparatus composed of a pickup having a wavelength λ of 405 nm and anumerical aperture NA of 0.85, and a recording signal is recorded on aland section L by a modulated signal, which is modulated by the 17PPmodulation method, wherein a minimum mark length (equivalent to 2T) is0.149 μm.

[0247] The information recording medium 5 recorded with theabove-mentioned recording signal is loaded into the reproducingapparatus 40 equipped with the pickup 50 having the wavelength λ of 405nm and the numerical aperture NA of 0.85 shown in FIG. 15. Byreproducing a land section L of the information recording medium 5, asignal having modulated amplitude, equivalent to (I8H−I8L)/I8H, of 0.52can be reproduced. Succeedingly, an error rate of reproduced signal isobtained and resulted in an excellent error rate of 2×10⁻⁵.Consequently, a data without any practical problems can be extracted.Further, an address error rate is about 1% at a recorded section, sothat an address data can be restored excellently.

[0248] In addition thereto, if an address error rate is less than 5%when reproducing after recorded on the recording layer 12, a dataincluding the least error can be restored through a process of errorcorrection. Accordingly, the address error rate of about 1% is suitablefor the information recording medium 5.

[0249] [Embodiment 2]

[0250] An information recording medium of an embodiment 2 is identicalto that of the embodiment 1 except for a modulation method for recordinga recording signal. The information recording medium of the embodiment 2is recorded with a recording signal modulated by the “D4, 6” modulationmethod, wherein a minimum mark length (equivalent to 2T) is 0.154 μm,and then reproduced as the same processes as those of the embodiment 1.

[0251] By reproducing a land section L of the information recordingmedium, a signal having modulated amplitude, equivalent to(I12H−I12L)/I12H, of 0.60 can be reproduced. Succeedingly, an error rateof reproduced signal is obtained and resulted in an excellent error rateof 8×10⁻⁶. Consequently, a data without any practical problems can beextracted. Further, an address error rate is about 1% at a recordedsection, so that an address data can be restored excellently.

[0252] [Embodiment 3]

[0253] An information recording medium of an embodiment 3 is identicalto that of the embodiment 1 except for a modulation method for recordinga recording signal. The information recording medium of the embodiment 3is recorded with a recording signal modulated by the “D8-15” modulationmethod, wherein a minimum mark length (equivalent to 3T) is 0.185 μm,and then reproduced as the same processes as those of the embodiment 1.

[0254] By reproducing a land section L of the information recordingmedium, a signal having modulated amplitude, equivalent to(I12H−I12L)/I12H, of 0.63 can be reproduced. Succeedingly, an error rateof reproduced signal is obtained and resulted in an excellent error rateof 4×10⁻⁶. Consequently, a data without any practical problems can beextracted. Further, an address error rate is about 1% at a recordedsection, so that an address data can be restored excellently.

[0255] [Embodiment 4]

[0256] An information recording medium 5 of an embodiment 4 is identicalto that of the embodiment 1 except for a modulation method for recordinga recording signal. The information recording medium 5 is recorded withan address data by the PM method shown in FIG. 10 on a land section L ina wobbling shape. The information recording medium 5 is recorded with arecording signal modulated by the 17PP modulation method, wherein aminimum mark length (equivalent to 2T) is 0.149 μm, and then reproducedas the same processes as those of the embodiment 1.

[0257] By reproducing a land section L of the information recordingmedium, a signal having modulated amplitude, equivalent to(I12H−I12L)/I12H, of 0.60 can be reproduced. Succeedingly, an error rateof reproduced signal is obtained and resulted in an excellent error rateof 2×10⁻⁶. Consequently, a data without any practical problems can beextracted. Further, an address error rate is about 0.1% at a recordedsection, so that an address data can be restored excellently.

[0258] [Embodiment 5]

[0259] An information recording medium 5 of an embodiment 5 is identicalto that of the embodiment 1 except for a modulation method for recordinga recording signal. An address data is recorded in a wobbling shape on aland section L of the information recording medium 5 by the base-bandmodulation method by Manchester code, wherein a phase having a phasedifference of ±π/2.5 is selected so as for a wave to be continuous at apoint of changing a frequency. The information recording medium 5 isrecorded with a recording signal modulated by the “D4, 6” modulationmethod, wherein a minimum mark length (equivalent to 2T) is 0.154 μm,and then reproduced as the same processes as those of the embodiment 1.

[0260] By reproducing a land section L of the information recordingmedium, a signal having modulated amplitude, equivalent to(I12H−I12L)/I12H, of 0.60 can be reproduced. Succeedingly, an error rateof reproduced signal is obtained and resulted in an excellent error rateof 8×10⁻⁶. Consequently, a data without any practical problems can beextracted. Further, an address error rate is about 0.1% at a recordedsection, so that an address data can be restored excellently.

COMPARATIVE EXAMPLE 1

[0261] By using the information recording medium 5 of the embodiment 1,it is recorded and reproduced as the same manner as those of theembodiment 1 except for recording on a groove section G.

[0262] By reproducing the groove section G of the information recordingmedium 5, a signal having modulated amplitude of 0.38 can be reproduced.Succeedingly, an error rate of reproduced signal is obtained andresulted in an error rate of 4×10⁻³. Consequently, a data, which is toodefective and has many bits being impossible to correct, can beextracted. Further, an address data is completely disordered. Therefore,the address data can not be extracted.

COMPARATIVE EXAMPLE 2

[0263] An information recording medium 5 of a comparative example 2 isidentical to that of the embodiment 1 except for a thick ness of lighttransmission layer 11, which is assigned to be 0.06 mm. The informationrecording medium 5 of the comparative example 2 is recorded andreproduced as the same manners as those of the embodiment 1.

[0264] By reproducing the information recording medium 5, a signalhaving modulated amplitude of 0.46 can be reproduced. However, an eyepattern is obscure. Succeedingly, an error rate of reproduced signal isobtained and resulted in an error rate of 6×⁻³. Consequently, a data,which is too defective and has many bits being impossible to correct,can be extracted. Further, the information recording medium 5 is easilyscratched by a test such that the objective lens 50 b is forced tocontact with and to slide on the information recording medium 5.Accordingly, the information recording medium 5 of the comparativeexample 2 is unsuitable for an information recording medium essentially.

COMPARATIVE EXAMPLE 3

[0265] An information recording medium of a comparative example 3 isidentical to that of the embodiment 1 except for a thick ness of lighttransmission layer 11, which is assigned to be 0.13 mm. The informationrecording medium of the comparative example 3 is recorded and reproducedas the same manners as those of the embodiment 1.

[0266] By reproducing the information recording medium, a signal havingmodulated amplitude of 0.38 can be reproduced. However, an eye patternis obscure. Succeedingly, an error rate of reproduced signal is obtainedand resulted in an error rate of 9×10⁻³. Consequently, a data, which istoo defective and has many bits being impossible to correct, can beextracted. Further, an address error rate is as many as 10% at arecorded section. Consequently, only an address data, which is defectiveand has many bits being impossible to correct, can be extracted.

[0267] The information recording medium of the present invention isexplained above with referring to the embodiments 1 through 5 and thecomparative examples 1 through 3.

[0268] In the present invention, modulated amplitude is assigned to bemore than 0.4 in consideration of that a reproduced signal is added witha noise inherent to a laser when reproducing an information recordingmedium 1. By this assignment, an information recording medium having asignal characteristic, which is compensated for an increased componentof laser noise, is provided.

[0269] With respect to a second method of compensating an increasedcomponent of noise inherent to a laser, there is existed a method ofregulating a reflectivity within a predetermined range. With payingattention to each “reflectivity” of the information recording mediums 1though 5, result of a study of “relationship between reflectivity anderror rate” is explained hereafter.

[0270] With respect to the information recording medium 5 shown in FIG.8 according to the fifth embodiment of the present invention, severalkinds of information recording mediums are manufactured by varying adepth (height difference between a groove section G and a land sectionL) of the microscopic pattern 20 formed on the substrate 13. Theseinformation recording mediums are reproduced by using the reproducingapparatus 40 composed of the light emitting element 50 a equipped with asemiconductor laser of gallium nitride system compound (its RIN is −125dB/Hz), and a relationship between a reflectivity and an error rate isexamined. Recording is performed under an ideal recording condition fordecreasing an error rate minimally.

[0271] A reflectivity can be expressed as an output of reproducedsignal. In a case of a phase change material, it is an index correlatingto brightness of a crystalline state. Actually, the informationrecording medium 5 is recorded with a modulated signal, which is theso-called (d, k) code mentioned above. A recording apparatus will beexplained later.

[0272] Loading the information recording medium 5 into the reproducingapparatus 40 in flat (without declination) and reproducing it obtains areflectivity from a signal having a maximum length used for a code byconnecting a reproduced signal in a DC system outputted form the pickup50 to an oscilloscope. In the case of the 8/16 modulation method usedfor a DVD disc, for example, the maximal length is 14T. By measuring anI14H as specified by the specification (JIS Standard X6241: 1997), areflectivity is calculated from an absolute reflectivity calibrationline.

[0273] Further, an error rate is obtained by measuring a reproducedsignal obtained through the demodulator 54.

[0274] The result is shown in FIG. 17.

[0275]FIG. 17 is a graph exhibiting a relation between a reflectivityand an error rate.

[0276] As shown in FIG. 17, there is existed a distinct relationshipbetween a reflectivity and an error rate. It is apparent that an errorrate remarkably increases in accordance with a reflectivity decreasing.If a practical error rate is assigned to be 3×10⁻⁴, which is specifiedfor a DVD disc, a necessary reflectivity becomes more than 2%.

[0277] Further, the information recording medium 5 may warp bytemperature change or like in circumstances of utilization of theinformation recording medium 5. Therefore, with assuming that adeclination of approximate 0.7 degree is possible to occur as a samesituation as a DVD disc, an error rate increases due to coma aberration,which is complexly produced by a wavelength λ within a range of 350 to450 nm, an NA within a range of 0.75 to 0.9 and a thickness of the lighttransmission layer 11 within a range of 0.07 to 0.12 mm.

[0278] By the result of measurement, it is found that the error rate of3×10⁻⁴ at the declination of 0.7 degree is equivalent to an error rateof 0.7×10⁻⁴ at the declination of zero degree. In other words, the errorrate of 0.7×10⁻⁴ is essential in consideration of a possible declinationwhen using the information recording medium 5 practically. Accordingly,it is understood that a practical reflectivity is more than 5%.

[0279] As mentioned above, in the case that a semiconductor laser ofgallium nitride system compound is used for a light emitting element, anerror rate can be reduced to a practical level as low as that of the DVDdisc specification if a reflectivity of the information recording medium5 is assigned to be more than 5% in consideration of a noise being addedto a reproduced signal. Further, it is found by experiments that acorrelation between reflectivity and error rate such as shown in FIG. 17can be obtained as a similar result by using any of the modulationmethods mentioned above.

[0280] A maximum mark length can vary by a modulation method. However, asignal output almost saturates at more than 6T by these modulationmethods and converges to a certain value. Consequently, a reflectivityobtained by recording the information recording medium 1 by the 17PPmodulation method, for example, and another reflectivity obtained by the8/16 modulation method become a same value as each other.

[0281] In consideration of a reproduction characteristic of informationrecording medium, the information recording mediums 1 through 5 of whichreflectivity is assigned to be more than 5% according to the presentinvention are explained hereinbefore.

[0282] In consideration of general characteristics of a recordingapparatus and a reproducing apparatus, which are equipped with asemiconductor laser of gallium nitride system compound as a lightemitting element, and physical characteristics of the recording layer 12or 123 composed of a phase change material totally, a practical range ofreflectivity necessary for realizing a total system is explained next.

[0283] An output of a semiconductor laser of gallium nitride systemcompound is 30 mW maximally. Generally, an output of light emittingelement falls down to almost one fifth of original output of the lightemitting element inside a recording apparatus due to a couplingefficiency of optical element, which is used for a wavelength λ beingwithin a range of 350 to 450 nm. In other words, a laser power becomes 6mW on each surface of the information recording mediums 1 through 5 eventhough a laser having an output of 30 mW is used. On the contrarily, itis desirable that a recording power is assigned to be higher as high aspossible in order to realize excellent phase change recording incontrast. Therefore, it is necessary for the information recordingmediums 1 through 5 to be recorded by a recording power of about 6 mW.It is necessary for absorptivity and transmissivity of the recordinglayer 12 or 123 of the information recording mediums 1 through 5 to berelatively higher value therefor.

[0284] Noise of a semiconductor laser of gallium nitride system compoundand increasing of noise of a reproducing apparatus equipped with such asemiconductor laser are explained hereinbefore. However, it is necessaryto pay attention to that noise depends upon a reproduction power. When alaser noise is measured by varying a reproduction power, it is foundthat noise increases in a lower laser power by using a semiconductorlaser of gallium nitride system compound, particularly, it is found thatthere is existed a critical point at the reproduction power of 0.35 mWon a surface of information recording medium. In other words, if areproduction power is below 0.35 mW, noise increases remarkably.Therefore, it is necessary for a reproduction power of the informationrecording mediums 1 through 5 to be more than 0.35 mW.

[0285] With respect to physical characteristics of the recording layer12 or 123, if a reproduction power is increased, the recording layer isthermally damaged and there is existed a phenomenon such that a recordmark M disappears. Particularly, in a case that a wavelength λ is withinthe range of 350 to 450 nm, energy density of a spot S to be formed onan information recording medium becomes larger than that of a redsemiconductor laser (of which wavelength λ is within a range of 635 to830 nm, for example). Therefore, a reproduction power is assigned to belower. However, since a minimum reproduction power is limited asmentioned above, a permitted limit of reproduction power is obliged tobe narrower. In order to increase resistivity for reproduction power,that is, in order to assign a reproduction power to be higher, it isnecessary for absorptivity and transmissivity of the recording layer 12or 123 of the information recording mediums 1 through 5 to be relativelylower value.

[0286] In consideration of general characteristics of a recordingapparatus and a reproducing apparatus, which are equipped with asemiconductor laser of gallium nitride system compound as a lightemitting element, and physical characteristics of the recording layer 12or 123 composed of a phase change material totally, as mentioned above,a recording power is assumed to be about 6 mW and a reproduction poweris necessary to be more than 0.35 mW. Further, an information recordingmedium of which record mark M on the recording layer 12 or 123 is hardlyerased by the reproduction power of more than 0.35 mW is required. Inorder to satisfy these various limits, it is necessary for absorptivityand transmissivity of the recording layer 12 or 123 of the informationrecording mediums 1 through 5 to be relatively higher value with respectto a material for the recording layer 12 or 123 of the informationrecording mediums 1 through 5 due to limitation for recording power.Furthermore, it is necessary for the absorptivity and transmissivity tobe relatively a lower value due to limitation of resistivity forreproduction power.

[0287] In other words, it is necessary for absorptivity andtransmissivity to be set within a predetermined range. A total amount ofabsorptivity, transmissivity and reflectivity is one. Therefore, it isalso necessary for the reflectivity to be set within a predeterminedrange.

[0288] A range of reflectivity satisfying the above-mentioned variouslimits is experimentally studied and a range of 12 to 26% is found.Processes of experimental study are definitely explained as embodiments6 through 12 and comparative examples 4 and 5 hereinafter.

[0289] [Embodiments 6 through 12]

[0290]FIG. 18 is a table showing reflectivity and reproductioncharacteristics of embodiments 6 through 12 and comparative examples 4and 5.

[0291] Polycarbonate having a thickness of 1.1 mm is used for asubstrate 13 of a phase change type information recording medium 5.Further, the information recording medium 5 is manufactured by usingmaterials such as Ag₉₈Pd₁Cu₁ for a reflective layer 121, ZnS—SiO₂ (inthe proportion of 80:20 in mol %) for a first protective layer 122,Ge₈Sb₆₉Te₂₃ for a recording layer 123 and ZnS—SiO₂ (in the proportion of80:20 in mol %) for a second protective layer 124, wherein each layer isformed in a certain film thickness shown in FIG. 18. Finally,polycarbonate having a thickness of 0.10 mm is laminated on the secondprotective layer 124 as a light transmission layer 11. Consequently, theinformation recording medium 5 is completed.

[0292] An address data is recorded in a wobbling shape on a land sectionL of the information recording medium 5 by the frequency modulationmethod, wherein a phase having a phase difference of ±π/2.5 is selectedso as for a wave to be continuous at a point of changing a frequency.

[0293] The information recording medium 5 is designed with assuming thatit is recorded by using a light beam having a wavelength λ of 405 nm andan objective lens having a numerical aperture NA of 0.85, and a pitch Pbetween land sections L is 0.32 μm. The reflective layer 121 andrecording layer 123 are formed in an atmosphere of 5 mTorr of argon gasby the DC sputtering, wherein a vacuum chamber used for sputtering ispreviously evacuated as low as less than 1×10⁻⁶ Torr.

[0294] Further, the completed information recording medium 5 isinitialized such that the recording layer 123 is changed in phase froman amorphous state low in reflectivity to a crystalline state high inreflectivity by irradiating a laser beam from the light transmissionlayer 11 side.

[0295] The information recording medium 5 is loaded into a recordingapparatus composed of a pickup having a wavelength λ of 405 nm and anumerical aperture NA of 0.85, and a recording signal is recorded on aland section L by a modulated signal, which is modulated by the 17PPmodulation method, wherein a minimum mark length (equivalent to 2T) is0.160 μm. Conditions for recording are as follows: 6.0 mW of recordingpower, 2.6 mW of bias power, 0.1 mW of bottom power between multi-pulsesand bottom power of cooling pulse, and 5.3 m/s of linear velocity.

[0296] Further, recording is a so-called recording by multi-pulsesmethod, which adopts a three-value power modulation such that each widthof a head pulse and a succeeding pulse is 0.4 times the recording period1T and a width of cooling pulse is 0.4 times the recording period 1T.

[0297] The information recording medium 5 recorded with theabove-mentioned recording signal is loaded into the reproducingapparatus 40 equipped with the pickup 50 having the wavelength λ of 405nm and the numerical aperture NA of 0.85 shown in FIG. 15. Items to beevaluated are as follows: reflectivity, modulated amplitude, equivalentto (I8H−I8L)/I8H, reproduction laser power at limit of deterioration,reproduction error rate of record mark M and address error rate. Thereproduction laser power at limit of deterioration is obtained bymeasuring a power such that reproducing the information recording medium5 at the reproduction power of 0.3 mW first, increasing the reproductionpower from 0.3 mW gradually, and measure a power when it is recognizedthat reproduction is deteriorated. The reproduction laser power at limitof deterioration, reproduction error rate and address error rate out ofthe items to be evaluated are judged by a reference value and determinedto be acceptable or not.

[0298] With respect to a standard for judging the reproduction laserpower at limit of deterioration, one can be reproduced by thereproduction power of more than 0.35 mW is acceptable (∘) and anothercan not be reproduced is not acceptable (×). With respect to a standardfor judging the reproduction error rate, one can be reproduced by theerror rate of less than 0.7×10⁻⁴ is acceptable (∘) and another can notbe reproduced is not acceptable (×). Further, with respect to a standardfor judging the address error rate, one can be reproduced by the errorrate of less than 5% (it is a limit of restoration by an errorcorrection) is acceptable (∘) and another can not be reproduced is notacceptable (×). Actual values of reflectivity, modulated amplitude andreproduction laser power at limit of deterioration, and judgment resultof reproduction laser power at limit of deterioration, reproductionerror rate and address error rate are summarized in FIG. 18. In FIG. 18,“Emb.” and “Comp.” represent “Embodiment” and “comparative example”respectively.

[0299] As shown in FIG. 18, each information recording medium 5manufactured by having a reflectivity within a range of 12 to 26%according to the embodiments 6 through 12 is excellent in deterioratedreproduction, reproduction error rate and address error rate.Consequently, the information recording medium according to theembodiments 6 through 12 can satisfy performance as a total system.

COMPARATIVE EXAMPLE 4

[0300] An information recording medium of which each layer is altered soas for a reflectivity to be 11.0% is prepared for the informationrecording medium 5 according to the comparative example 4 and evaluatedas the same manner as mentioned above in the embodiments 6 through 12. Aresult of evaluation is listed in FIG. 18.

[0301] According to the information recording medium 5 of thecomparative example 4, reproduction is deteriorated at the reproductionpower of 0.34 mW. Therefore, it is judged that sensitivity of therecording layer 123 is too high. Accordingly, an information recordingmedium having a reflectivity of less than 11% is not suitable for atotal system.

COMPARATIVE EXAMPLE 5

[0302] An information recording medium of which each layer is altered soas for a reflectivity to be 28.2% is prepared for the informationrecording medium 5 according to the comparative example 5 and evaluatedas the same manner as mentioned above in the embodiments 6 through 12. Aresult of evaluation is listed in FIG. 18.

[0303] In a case of the comparative example 5, there is not existed aproblem of deteriorated reproduction. However, the reproduction errorrate is high and resulted in defective. It is supposed to be a causethat the modulated amplitude is too small as low as 0.389. In otherwords, it is supposed that sensitivity of the recording layer 123 is toolow to be recorded in sufficient contrast. Therefore, an informationrecording medium having a reflectivity of more than 28% is not suitablefor a total system.

[0304] According to the evaluation result of the embodiments 6 through12 and the comparative examples 4 and 5, it is understood that a rangeof reflectivity suitable for a total system is 12 to 26%.

[0305] With referring to FIG. 17, the embodiments 6 through 12, thecomparative examples 4 and 5 and FIG. 18, the information recordingmediums 1 through 5 are explained hereinbefore. According to the presentinvention, in consideration of that noise inherent to a laser is addedto a reproduced signal while reproducing the information recordingmedium 1, the reflectivity is assigned to be more than 5%, preferably tobe within a range of 12 to 26%. Accordingly, an information recordingmedium having a signal characteristic of compensating an increasedcomponent caused by laser noise is provided.

[0306] The reproducing apparatus 40 shown in FIG. 15 of the presentinvention and the information recording mediums 1 through 5 of thepresent invention, which are loaded therein, are explained above. Thefirst reproduction apparatus 40 explained hereinbefore is a reproducingapparatus for reading out information recorded in the recording layer 12or 123, particularly, can reproduce contents recorded continuously for along period of time. For example, it can be used for reproducing a HDTV(high definition television) program and a movie recorded by videoequipment.

[0307] With referring to FIG. 19, a second reproducing apparatus 41according to the present invention is explained next.

[0308] A case of using the information recording medium 1 as for aninformation recording medium is explained hereinafter. However, theother information recording mediums 2 through 5 is the same situation asthe information recording medium 1.

[0309] The second reproducing apparatus 41 is identical to the firstreproducing apparatus 40 shown in FIG. 15 except for being equipped withan auxiliary information demodulator 56 allocated between the pickup 50and the controller 60, wherein an auxiliary information is read out by apickup 50. It is a reproducing apparatus used for index reproducing aHDTV program and a movie in video recording and for index reproducing acomputer recorded with data.

[0310] As mentioned above, a signal transmitted from the pickup 50 andto the demodulator 54 is a total sum signal (that is, Ia+Ib+Ic+Id) ofoutput from all 4 sections of a 4-division light detector not shown,wherein each of Ia, Ib, Ic and Id corresponds to each output of a4-division light detector for a DVD disc defined by the JIS Standard No.X6241: 1997. On the other hand, another signal transmitted from thepickup 50 to the auxiliary information demodulator 56 is a differentialsignal (that is, “(Ia−Ib)−(Ic−Id)”) of output from the 4-division lightdetector in the radial direction. An auxiliary information recorded in ashape of wobbling groove on the information recording medium 1 can beextracted by monitoring the differential signal because the wobbling isformed in the radial direction.

[0311] With respect to an actual configuration of the auxiliaryinformation demodulator 56, it is composed of at least one of anamplitude modulation (AM) demodulator, a frequency modulation (FM)demodulator and a phase modulation (PM) demodulator. In a case of the AMdemodulator, an envelope detector circuit can be suitably used. In acase of the FM demodulator, a frequency detector circuit and asynchronous detector circuit can be suitably used. In a case of the PMdetector, a synchronous detector circuit, a delay detector circuit andan envelope detector circuit can be suitably used. A sum signal may leakin a differential signal in the radial direction although it is quitelittle. In order to avoid such leakage, a band pass filter tuned in afrequency band of the auxiliary information can be connected in front ofthe auxiliary information demodulator 56.

[0312] Operations of the second reproducing apparatus 41 are explainednext.

[0313] A reproducing light 70 is emitted from a light emitting element50 a of the pickup 50 and converged at the microscopic pattern 20 in theinformation recording medium 1. Actually, the reproducing light 70 isfocused on the microscopic pattern 20, which is allocated at a depth of0.07 to 0.12 mm equivalent to a thickness of the light transmissionlayer 11. Succeedingly, tracking of the reproducing light 70 isperformed to either one of the groove section G or the land section L.The tracking is performed with choosing a predetermined side. However,as mentioned above, choosing the land section L is most desirable.

[0314] Then, an auxiliary information is read out by transmitting thedifferential signal (“(Ia+Ib)−(Ic+Id)”) in the radial direction from thepickup 50 to the auxiliary information demodulator 56. At this moment,with paying attention to an address information out of various kinds ofauxiliary information, the auxiliary information is compared with anaddress for indexing a data inputted to a controller 60.

[0315] If the auxiliary information does not coincide with the address,the controller 60 sends a signal to a servo device 52 and directs tosearch. Searching is performed such that a number of rotations of amotor 51 is reset to a number of rotations, which is suitable for aradius between the motor 51 and the pickup 50, according to movement inthe radial direction of the pickup 50 while scanning the movement of thepickup 50 in the radial direction. During a process of scanning, anaddress outputted from the auxiliary information demodulator 56, whichreceives a differential signal from the pickup 50, is compared with acertain address. The searching is continued until they coincide witheach other. When they coincide, scanning in the radial direction isinterrupted and reproduction is switched over to continuousreproduction. An output from the demodulator 54, which is inputted withthe sum signal (Ia+Ib+Ic+Id), becomes a signal of a demodulated datastream obtained by indexing and is inputted to an interface (I/F) 55.Finally, a signal is outputted externally in accordance with controllingby the controller 60.

[0316] As mentioned above, the information recording medium 1 and thesecond reproducing apparatus 41 according to the present invention aredesigned for coping with the reproducing light 70, which is produced bythe light emitting element 50 a having single wavelength λ within therange of 350 to 450 nm and the objective lens 50 b having the numericalaperture NA of 0.75 to 0.9. Therefore, the second reproducing apparatuscan preferably reproduce an auxiliary information and perform indexreproduction of a data stream in conjunction with reproducing theinformation recording medium 1 preferably.

[0317] With referring to FIG. 20, a recording apparatus 90 according tothe present invention is explained, wherein the information recordingmedium 1 is used as an information recording medium for explainingfunctions and operations of the recording apparatus 90. However, theother information recording mediums 2 through 5 are the same situationsas the information recording medium 1.

[0318]FIG. 20 is a block diagram of a recording apparatus according tothe present invention.

[0319] As shown in FIG. 20, the recording apparatus 90 is similar to thesecond reproducing apparatus 41 shown in FIG. 19 except for that thedemodulator 54 is replaced with a modulator 82 for modulating anoriginal data and a waveform converter 83 for transforming a modulatedsignal from the modulator 82 into a form suitable for recording on theinformation recording medium 1, which are connected in series. Furtherthe I/F 55 is replaced with an interface (I/F) 81 for receiving anexternal signal to be recorded.

[0320] The recording apparatus 90 is an apparatus for recording acomputer data, for example, at a predetermined address newly orrecording a HDTV program or a movie continuously from a predeterminedaddress as a video recording.

[0321] The modulator 82 is a modulator of converting an 8-bit originaldata into 16 bits, in the case of the 8/16 modulation (EFM plus) methodfor a DVD disc. The waveform converter 82 transforms a modulated signalreceived from the modulator 82 into a form suitable for recording on theinformation recording medium 1. Actually, the waveform converter 83 is aconverter, which converts the modulated signal into a recording pulsesatisfying a recording characteristic of the recording layer 12 of theinformation recording medium 1. For example, in a case that therecording layer 12 is composed of a phase change material, a so-calledmulti-pulse is formed. In other words, the modulated signal is dividedinto a unit of a channel bit or less and power is changed into arectangular waveform, wherein peak power, bottom power erase power and apulse time duration constituting a multi-pulse are assigned inaccordance with a direction of a controller 60.

[0322] Operations of the recording apparatus 90 are explained next.

[0323] A reproducing light 70 is emitted from a light emitting element50 a of a pickup 50 and converged at the microscopic pattern 20 in theinformation recording medium 1. Actually, the reproducing light 70 isfocused on the microscopic pattern 20, which is allocated at a depth of0.07 to 0.12 mm equivalent to a thickness of the light transmissionlayer 11. Succeedingly, tracking of the reproducing light 70 isperformed to either one of the groove section G or the land section L.The tracking is performed with choosing a predetermined side. However,as mentioned above, choosing the land section L is most desirable. Then,an auxiliary information is read out by transmitting the differentialsignal (“(Ia+Ib)−(Ic+Id)”) in the radial direction from the pickup 50 toan auxiliary information demodulator 56.

[0324] At this moment, with paying attention to an address informationout of various kinds of auxiliary information, the auxiliary informationis compared with an address for indexing a data inputted to thecontroller 60. If the auxiliary information does not coincide with theaddress, the controller 60 sends a signal to a servo device 52 anddirects to search. Searching is performed such that a number ofrotations of a motor 51 is reset to a number of rotations, which issuitable for a radius between the motor 51 and the pickup 50, accordingto movement in the radial direction of the pickup 50 while scanning themovement of the pickup 50 in the radial direction.

[0325] During a process of scanning, an address outputted from theauxiliary information demodulator 56, which receives a differentialsignal from the pickup 50, is compared with a certain address. Thesearching is continued until they coincide with each other. When theycoincide, scanning in the radial direction is interrupted andreproduction is switched over to continuous reproduction. In otherwords, a data inputted from the I/F 81 is modulated by the modulator 82in accordance with controlling by the controller 60. Succeedingly, thedata modulated by controlling of the controller 60 is inputted to thewaveform converter 83 and converted into a format suitable forrecording, and then outputted to a pickup 50.

[0326] In the pickup 50, a recording light 80 of which a recording poweris altered to that assigned by the waveform converter 83 is generatedand irradiated on the information recording medium 1. Consequently,recording at a predetermined address on the information recording medium1 is performed. It is possible that the differential signal(“(Ia+Ib)−(Ic+Id)”) in the radial direction is read out by the recordinglight 80, and an address can be extracted from the auxiliary informationdemodulator 56 even while recording. Therefore, a regional recordinglimited as far as an address desired by a user can be realized.

[0327] As mentioned above, the information recording medium 1 and therecording apparatus 90 according to the present invention are designedfor coping with the reproducing light 70 and the recording light 80,which are generated by the light emitting element 50 a having singlewavelength λ within the range of 350 to 450 nm and an objective lens 50b having the numerical aperture NA of 0.75 to 0.9. Therefore, therecording apparatus 90 can preferably record on the informationrecording medium 1 and, at the same time can reproduce an auxiliaryinformation, and then perform random indexing for recording.

[0328] The information recording mediums 1 through 5, the first andsecond reproducing apparatuses 40 and 41 and the recording apparatus 90are explained in details hereinbefore. Further, in the embodiments ofthe present invention, fundamental areas of the present invention areexplained. However, it is apparent that many changes, modifications andvariations in the arrangement of equipment and devices and in materialswithout departing from the invention concept disclosed herein. Forexample, an information recording medium having multi-layers (forinstance, triple and quadruple layers) of a set of the recording layer 7and the light transmission layer 8 laminated together can be applicableother than the information recording medium 1 having a single layer anddouble layers of the microscopic pattern 20.

[0329] Furthermore, with respect to the first and second reproducingapparatus 40 and 41 and the recording apparatus 90, it is also apparentthat each operation of them is not limited to those mentioned abovewithout departing the invention concept disclosed herein. For example, areproducing method and a recording method, which derive from replacingeach operation of the first and second reproducing apparatuses 40 and 41and the recording apparatus 90 with each step of reproducing andrecording processes, can be introduced for the present invention.Moreover, it is apparent that a computer program, which performs eachstep of the reproducing method, and another computer program, whichperforms each step of the reproducing method, are included in thepresent invention.

[0330] [Effect of the Invention]

[0331] As mentioned above, according to an aspect of the presentinvention, there provided an information recording medium, which is atleast composed of a substrate having a microscopic pattern constitutedby a shape of continuous substance of approximately parallel groovesformed with a groove section and a land section alternately, a recordinglayer formed on the microscopic pattern and a light transmission layerformed on the recording layer. Further, the microscopic pattern isformed with having a relation of P<λ<NA and a thickness of the lighttransmission layer is within a range of 0.07 to 0.12 mm, wherein P is apitch of the groove section or the land section, λ is a wavelength ofreproducing light beam and NA is a numerical aperture of objective lens.Therefore, an information recording medium, which can reduce cross eraseand also be recorded in higher density, can be obtained. Furthermore,recording in accordance with difference of reflectivity or phasedifference is performed by assigning modulated amplitude to be more than0.4, so that an error rate can be decreased to a practical level.

[0332] According to another aspect of the present invention, thereprovided a reproducing apparatus for reproducing an informationrecording medium, which is composed of a substrate having a microscopicpattern constituted by a shape of continuous substance of approximatelyparallel grooves formed with a groove section and a land sectionalternately. The reproducing apparatus is at least composed of a lightemitting element of which a wavelength of reproducing light is A nm, andhaving RIN (relative intensity noise) of less than −125 dB/Hz and anobjective lens having a numerical aperture NA. Further, the λ is withina range of 350 to 450 nm and the NA is within a range of 0.75 to 0.9.Furthermore, the reproducing light is irradiated on either one of theland section and the groove section. Therefore, cross erase can bereduced.

[0333] In the information recording medium according to the presentinvention, an auxiliary information such as an address data is recordedin shape on a part of or all over the microscopic pattern by anamplitude modulation (AM) method, so that an information can bedemodulated even in a low C/N (carrier to noise ratio) circumstance.Further, an auxiliary information such as an address data is recorded inshape on a part of or all over the microscopic pattern by a frequencymodulation (FM) method, so that an information can be demodulated by asimplified circuit. Particularly, by using the FM method selected with aproper phase, which is suitable for two waves to be connectedcontinuously at a point where their frequencies change over, areproduction envelope becomes approximately constant and stablereproduction can be realized. Furthermore, an auxiliary information suchas an address data is recorded in shape on a part of or all over themicroscopic pattern by a phase modulation (PM) method, so that aninformation can be demodulated by a synchronous detection even in a lowC/N circumstance. In particular, if phase difference between a highfrequency component and a low frequency component is assigned to be±π/2.5, excellent signal demodulation can be realized by the synchronousdetection even in a low C/N circumstance.

[0334] In addition thereto, an auxiliary information such as an addressdata can be improved in stability of readout, if the auxiliaryinformation is previously formed in a data modulated in a base-band, inwhich a number of same bits continuing is limited to be less than apredetermined quantity.

[0335] It should be understood that many modifications and adaptationsof the invention will become apparent to those skilled in the art and itis intended to encompass such obvious modifications and changes in thescope of the claims appended hereto.

What is claimed is:
 1. An information recording medium at leastcomprising: a substrate having a microscopic pattern, which isconstituted by a shape of continuous substance of approximately parallelgrooves formed with a groove section and a land section alternately; arecording layer formed on the microscopic pattern; and a lighttransmission layer formed on the recording layer, the informationrecording layer is characterized in that the microscopic pattern isformed so as to satisfy a relation of P<λ<NA and a thickness of thelight transmission layer is within a range of 0.07 to 0.12 mm, wherein Pis a pitch of the groove section or the land section, λ is a wavelengthof reproducing light beam and NA is a numerical aperture of objectivelens.
 2. The information recording medium in accordance with claim 1,wherein a record based on at least one of reflectivity difference andphase difference is performed onto either one of the groove section andthe land section.
 3. The information recording medium in accordance withclaim 1, wherein the wavelength λ is within a range of 350 to 450 nm andthe numerical aperture NA is within a range of 0.75 to 0.9.
 4. Theinformation recording medium in accordance with claim 2, whereinrecording in accordance with at least one of the reflectivity differenceand the phase difference is performed so as for the modulated amplitudeto be more than 0.4.
 5. The information recording medium in accordancewith claim 2, wherein recording in accordance with at least one of thereflectivity difference and the phase difference is performed so as forthe reflectivity to be more than 5%.
 6. The information recording mediumin accordance with claim 1, wherein the recording layer is formed by aphase change material.
 7. A reproducing apparatus for reproducing aninformation recording medium at least comprising: a substrate having amicroscopic pattern, which is constituted by a shape of continuoussubstance of approximately parallel grooves formed with a groove sectionand a land section alternately; a recording layer formed on themicroscopic pattern; and a light transmission layer formed on therecording layer, wherein the information recording layer ischaracterized in that the microscopic pattern is formed so as to satisfya relation of P<λ<NA and a thickness of the light transmission layer iswithin a range of 0.07 to 0.12 mm, and wherein P is a pitch of thegroove section or the land section, λ is a wavelength of reproducinglight beam and NA is a numerical aperture of objective lens, thereproducing apparatus comprising: a pickup composed of a light emittingelement having a wavelength of λ within a range of 350 to 450 nm and anobjective lens having a numerical aperture of NA within a range of 0.75to 0.9 for reading out reflected light from the information recordingmedium; a motor for rotating the information recording medium; servomeans for controlling to drive the pickup and the motor; a turntable forsupporting the information recording medium while rotating; demodulatormeans for demodulating an information signal read out by the pickup;interface (I/F) means for transmitting a signal demodulated by thedemodulator externally; and controlling means for controlling thereproducing apparatus totally.
 8. The reproducing apparatus inaccordance with claim 7, the recording apparatus further comprising anauxiliary information demodulator for demodulating a differential signaloutputted from the pickup.
 9. A recording apparatus for recording anoriginal information signal on an information recording medium at leastcomprising: a substrate having a microscopic pattern, which isconstituted by a shape of continuous substance of approximately parallelgrooves formed with a groove section and a land section alternately; arecording layer formed on the microscopic pattern; and a lighttransmission layer formed on the recording layer, wherein theinformation recording layer is characterized in that the microscopicpattern is formed so as to satisfy a relation of P<λ<NA and a thicknessof the light transmission layer is within a range of 0.07 to 0.12 mm,and wherein P is a pitch of the groove section or the land section, λ isa wavelength of reproducing light beam and NA is a numerical aperture ofobjective lens, the recording apparatus comprising: a pickup composed ofa light emitting element having a wavelength of λ within a range of 350to 450 nm and an objective lens having a numerical aperture of NA withina range of 0.75 to 0.9 for reading out reflected light from andrecording on the information recording medium; a motor for rotating theinformation recording medium; servo means for controlling to drive thepickup and the motor; a turntable for supporting the informationrecording medium while rotating; interface (I/F) means for receiving theoriginal information signal to be recorded; modulator means formodulating the original information signal; waveform converter means forconverting the original information signal into a format suitable for arecording characteristic of the recording layer of the informationrecording medium; auxiliary information demodulator means fordemodulating a differential signal outputted from the pickup; andcontrolling means for controlling the recording apparatus totally.